Configuring IP Unicast Routing

Configuring IP Unicast Routing
Configuring IP Unicast Routing
• Finding Feature Information, page 2
• Information About Configuring IP Unicast Routing, page 2
• Information About IP Routing, page 2
• How to Configure IP Routing, page 5
• How to Configure IP Addressing, page 6
• Monitoring and Maintaining IP Addressing, page 30
• How to Configure IP Unicast Routing, page 31
• Information About RIP, page 33
• How to Configure RIP, page 33
• Information About OSPF, page 41
• Monitoring OSPF, page 57
• Information About EIGRP, page 58
• How to Configure EIGRP, page 59
• Monitoring and Maintaining EIGRP, page 68
• Information About BGP, page 69
• How to Configure BGP, page 70
• Monitoring and Maintaining BGP, page 100
• Information About ISO CLNS Routing, page 102
• How to Configure ISO CLNS Routing, page 102
• Monitoring and Maintaining ISO IGRP and IS-IS, page 114
• Information About Multi-VRF CE, page 116
• How to Configure Multi-VRF CE, page 119
• Configuring Unicast Reverse Path Forwarding, page 138
• Protocol-Independent Features, page 138
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Configuring IP Unicast Routing
Finding Feature Information
• Monitoring and Maintaining the IP Network, page 162
• Additional References for Configuring IP Unicast Routing, page 163
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and
feature information, see Bug Search Tool and the release notes for your platform and software release. To
find information about the features documented in this module, and to see a list of the releases in which each
feature is supported, see the feature information table at the end of this module.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support.
To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not
required.
Information About Configuring IP Unicast Routing
This module describes how to configure IP Version 4 (IPv4) unicast routing on the switch.
A switch stack operates and appears as a single router to the rest of the routers in the network. Basic routing
functions, including static routing and the Routing Information Protocol (RIP), are available with .
Note
In addition to IPv4 traffic, you can also enable IP Version 6 (IPv6) unicast routing and configure interfaces
to forward IPv6 traffic.
Information About IP Routing
In some network environments, VLANs are associated with individual networks or subnetworks. In an IP
network, each subnetwork is mapped to an individual VLAN. Configuring VLANs helps control the size of
the broadcast domain and keeps local traffic local. However, network devices in different VLANs cannot
communicate with one another without a Layer 3 device (router) to route traffic between the VLAN, referred
to as inter-VLAN routing. You configure one or more routers to route traffic to the appropriate destination
VLAN.
This figure shows a basic routing topology. Switch A is in VLAN 10, and Switch B is in VLAN 20. The router
has an interface in each VLAN.
Figure 1: Routing Topology Example
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Configuring IP Unicast Routing
Types of Routing
When Host A in VLAN 10 needs to communicate with Host B in VLAN 10, it sends a packet addressed to
that host. Switch A forwards the packet directly to Host B, without sending it to the router.
When Host A sends a packet to Host C in VLAN 20, Switch A forwards the packet to the router, which
receives the traffic on the VLAN 10 interface. The router checks the routing table, finds the correct outgoing
interface, and forwards the packet on the VLAN 20 interface to Switch B. Switch B receives the packet and
forwards it to Host C.
Types of Routing
Routers and Layer 3 switches can route packets in these ways:
• By using default routing
• By using preprogrammed static routes for the traffic
• By dynamically calculating routes by using a routing protocol
Default routing refers to sending traffic with a destination unknown to the router to a default outlet
or destination.
Static unicast routing forwards packets from predetermined ports through a single path into and out of a
network. Static routing is secure and uses little bandwidth, but does not automatically respond to changes in
the network, such as link failures, and therefore, might result in unreachable destinations. As networks grow,
static routing becomes a labor-intensive liability.
Beginning with Cisco IOS release 12.2(58)SE, switches running the LAN base feature set support 16
user-configured static routes, in addition to any default routes used for the management interface. The LAN
base image supports static routing only on SVIs and only when the switch is running the default SDM template.
Dynamic routing protocols are used by routers to dynamically calculate the best route for forwarding traffic.
There are two types of dynamic routing protocols:
• Routers using distance-vector protocols maintain routing tables with distance values of networked
resources, and periodically pass these tables to their neighbors. Distance-vector protocols use one or a
series of metrics for calculating the best routes. These protocols are easy to configure and use.
• Routers using link-state protocols maintain a complex database of network topology, based on the
exchange of link-state advertisements (LSAs) between routers. LSAs are triggered by an event in the
network, which speeds up the convergence time or time required to respond to these changes. Link-state
protocols respond quickly to topology changes, but require greater bandwidth and more resources than
distance-vector protocols.
Distance-vector protocols supported by the switch are Routing Information Protocol (RIP), which uses a single
distance metric (cost) to determine the best path and Border Gateway Protocol (BGP), which adds a path
vector mechanism. The switch also supports the Open Shortest Path First (OSPF) link-state protocol and
Enhanced IGRP (EIGRP), which adds some link-state routing features to traditional Interior Gateway Routing
Protocol (IGRP) to improve efficiency.
Note
On a switch or switch stack, the supported protocols are determined by the software running on the active
switch. If the switch is running the LAN base feature set, you can configure 16 static routes on SVIs. All
other routing protocols require the IP services feature set.
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Configuring IP Unicast Routing
IP Routing and Switch Stacks
IP Routing and Switch Stacks
A Switch stack appears to the network as a single Switch, regardless of which Switch in the stack is connected
to a routing peer.
The stack master performs these functions:
• It initializes and configures the routing protocols.
• It sends routing protocol messages and updates to other routers.
• It processes routing protocol messages and updates received from peer routers.
• It generates, maintains, and distributes the distributed Cisco Express Forwarding (dCEF) database to all
stack members. The routes are programmed on all Switch in the stack bases on this database.
• The MAC address of the stack master is used as the router MAC address for the whole stack, and all
outside devices use this address to send IP packets to the stack.
• All IP packets that require software forwarding or processing go through the CPU of the stack master.
Stack members perform these functions:
• They act as routing standby Switch, ready to take over in case they are elected as the new stack master
if the stack master fails.
• They program the routes into hardware.
If a stack master fails, the stack detects that the stack master is down and elects one of the stack members to
be the new stack master. During this period, except for a momentary interruption, the hardware continues to
forward packets with no active protocols.
However, even though the Switch stack maintains the hardware identification after a failure, the routing
protocols on the router neighbors might flap during the brief interruption before the stack master restarts.
Routing protocols such as OSPF and EIGRP need to recognize neighbor transitions.
The router uses two levels of nonstop forwarding (NSF) to detect a Switch over, to continue forwarding
network traffic, and to recover route information from peer devices:
• NSF-aware routers tolerate neighboring router failures. After the neighbor router restarts, an NSF-aware
router supplies information about its state and route adjacencies on request.
• NSF-capable routers support NSF. When they detect a stack master change, they rebuild routing
information from NSF-aware or NSF-capable neighbors and do not wait for a restart.
The Switch stack supports NSF-capable routing for OSPF and EIGRP.
Upon election, the new stack master performs these functions:
• It starts generating, receiving, and processing routing updates.
• It builds routing tables, generates the CEF database, and distributes it to stack members.
• It uses its MAC address as the router MAC address. To notify its network peers of the new MAC address,
it periodically (every few seconds for 5 minutes) sends a gratuitous ARP reply with the new router MAC
address.
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How to Configure IP Routing
Note
If you configure the persistent MAC address feature on the stack and the stack master
changes, the stack MAC address does not change for the configured time period. If the
previous stack master rejoins the stack as a member Switch during that time period, the
stack MAC address remains the MAC address of the previous stack master.
• It attempts to determine the reachability of every proxy ARP entry by sending an ARP request to the
proxy ARP IP address and receiving an ARP reply. For each reachable proxy ARP IP address, it generates
a gratuitous ARP reply with the new router MAC address. This process is repeated for 5 minutes after
a new stack master election.
Note
Caution
When a stack master is running the IP services feature set, the stack can run all supported
protocols, including Open Shortest Path First (OSPF), and Enhanced IGRP (EIGRP)
and Border Gateway Protocol (BGP). If the stack master fails and the new elected stack
master is running the IP base or LAN base feature set, these protocols will no longer
run in the stack.
Partitioning of the Switch stack into two or more stacks might lead to undesirable
behavior in the network.
How to Configure IP Routing
By default, IP routing is disabled on the Switch, and you must enable it before routing can take place. For
detailed IP routing configuration information, see the Cisco IOS IP Configuration Guide.
In the following procedures, the specified interface must be one of these Layer 3 interfaces:
• A routed port: a physical port configured as a Layer 3 port by using the no switchport interface
configuration command.
• A switch virtual interface (SVI): a VLAN interface created by using the interface vlan vlan_id global
configuration command and by default a Layer 3 interface.
Note
If the Switch is running the LAN base feature set, static routes are supported only on
SVIs.
• An EtherChannel port channel in Layer 3 mode: a port-channel logical interface created by using the
interface port-channel port-channel-number global configuration command and binding the Ethernet
interface into the channel group. For more information, see the “Configuring Layer 3 EtherChannels”
chapter in the Layer 2 Configuration Guide.
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How to Configure IP Addressing
Note
The switch does not support tunnel interfaces for unicast routed traffic.
All Layer 3 interfaces on which routing will occur must have IP addresses assigned to them.
Note
A Layer 3 switch can have an IP address assigned to each routed port and SVI.
The number of routed ports and SVIs that you can configure is not limited by software. However, the
interrelationship between this number and the number and volume of features being implemented might
have an impact on CPU utilization because of hardware limitations. To optimize system memory for
routing, use the sdm prefer routing global configuration command when running the IP base or IP services
feature set.
Configuring routing consists of several main procedures:
• To support VLAN interfaces, create and configure VLANs on the Switch or switch stack, and assign
VLAN membership to Layer 2 interfaces. For more information, see the "Configuring VLANs” chapter
in the VLAN Configuration Guide.
• Configure Layer 3 interfaces.
• Enable IP routing on the switch.
• Assign IP addresses to the Layer 3 interfaces.
• Enable selected routing protocols on the switch.
• Configure routing protocol parameters (optional).
Related Topics
Assigning IP Addresses to Network Interfaces, on page 8
How to Configure IP Addressing
A required task for configuring IP routing is to assign IP addresses to Layer 3 network interfaces to enable
the interfaces and allow communication with the hosts on those interfaces that use IP. The following sections
describe how to configure various IP addressing features. Assigning IP addresses to the interface is required;
the other procedures are optional.
Note
On switches running the LAN base feature set, you can only assign an IP address to an SVI and configure
a static unicast route on the interface. Other configurations are not supported.
• Default Addressing Configuration
• Assigning IP Addresses to Network Interfaces
• Configuring Address Resolution Methods
• Routing Assistance When IP Routing is Disabled
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Default IP Addressing Configuration
• Configuring Broadcast Packet Handling
• Monitoring and Maintaining IP Addressing
Default IP Addressing Configuration
Table 1: Default Addressing Configuration
Feature
Default Setting
IP address
None defined.
ARP
No permanent entries in the Address Resolution Protocol (ARP) cache.
Encapsulation: Standard Ethernet-style ARP.
Timeout: 14400 seconds (4 hours).
IP broadcast address
255.255.255.255 (all ones).
IP classless routing
Enabled.
IP default gateway
Disabled.
IP directed broadcast Disabled (all IP directed broadcasts are dropped).
IP domain
Domain list: No domain names defined.
Domain lookup: Enabled.
Domain name: Enabled.
IP forward-protocol
If a helper address is defined or User Datagram Protocol (UDP) flooding is
configured, UDP forwarding is enabled on default ports.
Any-local-broadcast: Disabled.
Spanning Tree Protocol (STP): Disabled.
Turbo-flood: Disabled.
IP helper address
Disabled.
IP host
Disabled.
IRDP
Disabled.
Defaults when enabled:
• Broadcast IRDP advertisements.
• Maximum interval between advertisements: 600 seconds.
• Minimum interval between advertisements: 0.75 times max interval
• Preference: 0.
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Assigning IP Addresses to Network Interfaces
Feature
Default Setting
IP proxy ARP
Enabled.
IP routing
Disabled.
IP subnet-zero
Disabled.
Assigning IP Addresses to Network Interfaces
An IP address identifies a location to which IP packets can be sent. Some IP addresses are reserved for special
uses and cannot be used for host, subnet, or network addresses. RFC 1166, “Internet Numbers,” contains the
official description of IP addresses.
An interface can have one primary IP address. A mask identifies the bits that denote the network number in
an IP address. When you use the mask to subnet a network, the mask is referred to as a subnet mask. To
receive an assigned network number, contact your Internet service provider.
Note
On switches running the LAN base image, you can only assign an IP address to an SVI and then configure
a static route for the SVI. The switch supports 16 user-configured static routes. See the “Configuring Static
Unicast Routes” section. No other routing configurations are supported.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if
prompted.
Example:
Switch> enable
Step 2
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 3
interface interface-id
Enters interface configuration mode, and specifies the Layer
3 interface to configure.
Example:
Note
Switch(config)# interface gigabitethernet
1/0/1
Only SVI interfaces are supported on switches
running the LAN base feature set.
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Assigning IP Addresses to Network Interfaces
Step 4
Command or Action
Purpose
no switchport
Removes the interface from Layer 2 configuration mode (if
it is a physical interface).
Example:
Switch(config-if)# no switchport
Step 5
ip address ip-address subnet-mask
Configures the IP address and IP subnet mask.
Example:
Switch(config-if)# ip address 10.1.5.1
255.255.255.0
Step 6
Enables the physical interface.
no shutdown
Example:
Switch(config-if)# no shutdown
Step 7
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 8
Verifies your entries.
show ip route
Example:
Switch# show ip route
Step 9
show ip interface [interface-id]
Verifies your entries.
Example:
Switch# show ip interface gigabitethernet
1/0/1
Step 10
show running-config
Verifies your entries.
Example:
Switch# show running-config
Step 11
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Step 12
On switches running the LAN base image, you can only
assign an IP address to an SVI and then configure a static
route for the SVI. The switch supports 16 user-configured
static routes. No other routing configurations are supported.
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Command or Action
Purpose
Related Topics
How to Configure IP Routing, on page 5
Using Subnet Zero
Subnetting with a subnet address of zero is strongly discouraged because of the problems that can arise if a
network and a subnet have the same addresses. For example, if network 131.108.0.0 is subnetted as
255.255.255.0, subnet zero would be written as 131.108.0.0, which is the same as the network address.
You can use the all ones subnet (131.108.255.0) and even though it is discouraged, you can enable the use of
subnet zero if you need the entire subnet space for your IP address.
Use the no ip subnet-zero global configuration command to restore the default and disable the use of subnet
zero.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password
if prompted.
Example:
Switch> enable
Step 2
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 3
ip subnet-zero
Enables the use of subnet zero for interface addresses
and routing updates.
Example:
Switch(config)# ip subnet-zero
Step 4
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
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Assigning IP Addresses to Network Interfaces
Step 5
Command or Action
Purpose
show running-config
Verifies your entries.
Example:
Switch# show running-config
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Classless Routing
By default, classless routing behavior is enabled on the Switch when it is configured to route. With classless
routing, if a router receives packets for a subnet of a network with no default route, the router forwards the
packet to the best supernet route. A supernet consists of contiguous blocks of Class C address spaces used to
simulate a single, larger address space and is designed to relieve the pressure on the rapidly depleting Class
B address space.
In the figure, classless routing is enabled. When the host sends a packet to 120.20.4.1, instead of discarding
the packet, the router forwards it to the best supernet route. If you disable classless routing and a router receives
packets destined for a subnet of a network with no network default route, the router discards the packet.
Figure 2: IP Classless Routing
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Assigning IP Addresses to Network Interfaces
In the figure , the router in network 128.20.0.0 is connected to subnets 128.20.1.0, 128.20.2.0, and 128.20.3.0.
If the host sends a packet to 120.20.4.1, because there is no network default route, the router discards the
packet.
Figure 3: No IP Classless Routing
To prevent the Switch from forwarding packets destined for unrecognized subnets to the best supernet route
possible, you can disable classless routing behavior.
Disabling Classless Routing
To prevent the Switch from forwarding packets destined for unrecognized subnets to the best supernet route
possible, you can disable classless routing behavior.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if
prompted.
Example:
Switch> enable
Step 2
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 3
no ip classless
Disables classless routing behavior.
Example:
Switch(config)#no ip classless
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Configuring Address Resolution Methods
Step 4
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 5
show running-config
Verifies your entries.
Example:
Switch# show running-config
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Step 7
To restore the default and have the switch forward packets
destined for a subnet of a network with no network default
route to the best supernet route possible, use the ip classless
global configuration command.
Configuring Address Resolution Methods
You can perform the following tasks to configure address resolution.
Address Resolution
You can control interface-specific handling of IP by using address resolution. A device using IP can have
both a local address or MAC address, which uniquely defines the device on its local segment or LAN, and a
network address, which identifies the network to which the device belongs.
Note
In a switch stack, network communication uses a single MAC address and the IP address of the stack.
The local address or MAC address is known as a data link address because it is contained in the data link
layer (Layer 2) section of the packet header and is read by data link (Layer 2) devices. To communicate with
a device on Ethernet, the software must learn the MAC address of the device. The process of learning the
MAC address from an IP address is called address resolution. The process of learning the IP address from
the MAC address is called reverse address resolution.
The Switch can use these forms of address resolution:
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Configuring Address Resolution Methods
• Address Resolution Protocol (ARP) is used to associate IP address with MAC addresses. Taking an IP
address as input, ARP learns the associated MAC address and then stores the IP address/MAC address
association in an ARP cache for rapid retrieval. Then the IP datagram is encapsulated in a link-layer
frame and sent over the network. Encapsulation of IP datagrams and ARP requests or replies on IEEE
802 networks other than Ethernet is specified by the Subnetwork Access Protocol (SNAP).
• Proxy ARP helps hosts with no routing tables learn the MAC addresses of hosts on other networks or
subnets. If the Switch (router) receives an ARP request for a host that is not on the same interface as the
ARP request sender, and if the router has all of its routes to the host through other interfaces, it generates
a proxy ARP packet giving its own local data link address. The host that sent the ARP request then sends
its packets to the router, which forwards them to the intended host.
The Switch also uses the Reverse Address Resolution Protocol (RARP), which functions the same as ARP
does, except that the RARP packets request an IP address instead of a local MAC address. Using RARP
requires a RARP server on the same network segment as the router interface. Use the ip rarp-server address
interface configuration command to identify the server.
For more information on RARP, see the Cisco IOS Configuration Fundamentals Configuration Guide
Defining a Static ARP Cache
ARP and other address resolution protocols provide dynamic mapping between IP addresses and MAC
addresses. Because most hosts support dynamic address resolution, you usually do not need to specify static
ARP cache entries. If you must define a static ARP cache entry, you can do so globally, which installs a
permanent entry in the ARP cache that the Switch uses to translate IP addresses into MAC addresses. Optionally,
you can also specify that the Switch respond to ARP requests as if it were the owner of the specified IP address.
If you do not want the ARP entry to be permanent, you can specify a timeout period for the ARP entry.
To remove an entry from the ARP cache, use the no arp ip-address hardware-address type global configuration
command. To remove all nonstatic entries from the ARP cache, use the clear arp-cache privileged EXEC
command.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if
prompted.
Example:
Switch> enable
Step 2
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
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Configuring Address Resolution Methods
Step 3
Command or Action
Purpose
arp ip-address hardware-address type
Associates an IP address with a MAC (hardware) address in
the ARP cache, and specifies encapsulation type as one of these:
Example:
• arpa—ARP encapsulation for Ethernet interfaces
Switch(config)# ip 10.1.5.1 c2f3.220a.12f4
arpa
• snap—Subnetwork Address Protocol encapsulation for
Token Ring and FDDI interfaces
• sap—HP’s ARP type
Step 4
arp ip-address hardware-address type [alias]
(Optional) Specifies that the switch respond to ARP requests
as if it were the owner of the specified IP address.
Example:
Switch(config)# ip 10.1.5.3 d7f3.220d.12f5
arpa alias
Step 5
interface interface-id
Enters interface configuration mode, and specifies the interface
to configure.
Example:
Switch(config)# interface gigabitethernet
1/0/1
Step 6
arp timeout seconds
(Optional) Sets the length of time an ARP cache entry will stay
in the cache. The default is 14400 seconds (4 hours). The range
is 0 to 2147483 seconds.
Example:
Switch(config-if)# arp 20000
Step 7
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 8
show interfaces [interface-id]
Verifies the type of ARP and the timeout value used on all
interfaces or a specific interface.
Example:
Switch# show interfaces gigabitethernet
1/0/1
Step 9
Views the contents of the ARP cache.
show arp
Example:
Switch# show arp
Step 10
Views the contents of the ARP cache.
show ip arp
Example:
Switch# show ip arp
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Configuring Address Resolution Methods
Step 11
Command or Action
Purpose
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Setting ARP Encapsulation
By default, Ethernet ARP encapsulation (represented by the arpa keyword) is enabled on an IP interface.
You can change the encapsulation methods to SNAP if required by your network.
To disable an encapsulation type, use the no arp arpa or no arp snap interface configuration command.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if
prompted.
Example:
Switch> enable
Step 2
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 3
interface interface-id
Enters interface configuration mode, and specifies the Layer
3 interface to configure.
Example:
Switch(config)# interface gigabitethernet
1/0/2
Step 4
arp {arpa | snap}
Example:
Switch(config-if)# arp arpa
Specifies the ARP encapsulation method:
• arpa—Address Resolution Protocol
• snap—Subnetwork Address Protocol
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Step 5
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 6
show interfaces [interface-id]
Verifies ARP encapsulation configuration on all interfaces
or the specified interface.
Example:
Switch# show interfaces
Step 7
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Enabling Proxy ARP
By default, the Switch uses proxy ARP to help hosts learn MAC addresses of hosts on other networks or
subnets.
To disable proxy ARP on the interface, use the no ip proxy-arp interface configuration command.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password
if prompted.
Example:
Switch> enable
Step 2
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
Step 3
interface interface-id
Enters interface configuration mode, and specifies the
Layer 3 interface to configure.
Example:
Switch(config)# interface gigabitethernet 1/0/2
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Configuring IP Unicast Routing
Routing Assistance When IP Routing is Disabled
Step 4
Command or Action
Purpose
ip proxy-arp
Enables proxy ARP on the interface.
Example:
Switch(config-if)# ip proxy-arp
Step 5
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 6
show ip interface [interface-id]
Verifies the configuration on the interface or all
interfaces.
Example:
Switch# show ip interface gigabitethernet 1/0/2
Step 7
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Routing Assistance When IP Routing is Disabled
These mechanisms allow the Switch to learn about routes to other networks when it does not have IP routing
enabled:
• Proxy ARP
• Default Gateway
• ICMP Router Discovery Protocol (IRDP)
Proxy ARP
Proxy ARP, the most common method for learning about other routes, enables an Ethernet host with no routing
information to communicate with hosts on other networks or subnets. The host assumes that all hosts are on
the same local Ethernet and that they can use ARP to learn their MAC addresses. If a Switch receives an ARP
request for a host that is not on the same network as the sender, the Switch evaluates whether it has the best
route to that host. If it does, it sends an ARP reply packet with its own Ethernet MAC address, and the host
that sent the request sends the packet to the Switch, which forwards it to the intended host. Proxy ARP treats
all networks as if they are local and performs ARP requests for every IP address.
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Configuring IP Unicast Routing
Routing Assistance When IP Routing is Disabled
Proxy ARP
Proxy ARP is enabled by default. To enable it after it has been disabled, see the “Enabling Proxy ARP” section.
Proxy ARP works as long as other routers support it.
Default Gateway
Another method for locating routes is to define a default router or default gateway. All non-local packets are
sent to this router, which either routes them appropriately or sends an IP Control Message Protocol (ICMP)
redirect message back, defining which local router the host should use. The Switch caches the redirect messages
and forwards each packet as efficiently as possible. A limitation of this method is that there is no means of
detecting when the default router has gone down or is unavailable.
Use the no ip default-gateway global configuration command to disable this function.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password
if prompted.
Example:
Switch> enable
Step 2
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
Step 3
ip default-gateway ip-address
Sets up a default gateway (router).
Example:
Switch(config)# ip default gateway 10.1.5.1
Step 4
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 5
Displays the address of the default gateway router to
verify the setting.
show ip redirects
Example:
Switch# show ip redirects
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Routing Assistance When IP Routing is Disabled
Step 6
Command or Action
Purpose
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
ICMP Router Discovery Protocol
Router discovery allows the Switch to dynamically learn about routes to other networks using ICMP router
discovery protocol (IRDP). IRDP allows hosts to locate routers. When operating as a client, the Switch
generates router discovery packets. When operating as a host, the Switch receives router discovery packets.
The Switch can also listen to Routing Information Protocol (RIP) routing updates and use this information to
infer locations of routers. The Switch does not actually store the routing tables sent by routing devices; it
merely keeps track of which systems are sending the data. The advantage of using IRDP is that it allows each
router to specify both a priority and the time after which a device is assumed to be down if no further packets
are received.
Each device discovered becomes a candidate for the default router, and a new highest-priority router is selected
when a higher priority router is discovered, when the current default router is declared down, or when a TCP
connection is about to time out because of excessive retransmissions.
ICMP Router Discovery Protocol (IRDP)
The only required task for IRDP routing on an interface is to enable IRDP processing on that interface. When
enabled, the default parameters apply.
You can optionally change any of these parameters. If you change the maxadvertinterval value, the holdtime
and minadvertinterval values also change, so it is important to first change the maxadvertinterval value,
before manually changing either the holdtime or minadvertinterval values.
Use the no ip irdp interface configuration command to disable IRDP routing.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if prompted.
Example:
Switch> enable
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Configuring IP Unicast Routing
Routing Assistance When IP Routing is Disabled
Step 2
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 3
interface interface-id
Enters interface configuration mode, and specifies the Layer 3
interface to configure.
Example:
Switch(config)# interface gigabitethernet
1/0/1
Step 4
Enables IRDP processing on the interface.
ip irdp
Example:
Switch(config-if)# ip irdp
Step 5
ip irdp multicast
(Optional) Sends IRDP advertisements to the multicast address
(224.0.0.1) instead of IP broadcasts.
Example:
Note
Switch(config-if)# ip irdp multicast
Step 6
ip irdp holdtime seconds
Example:
Switch(config-if)# ip irdp holdtime 1000
Step 7
ip irdp maxadvertinterval seconds
This command allows for compatibility with Sun
Microsystems Solaris, which requires IRDP packets to be
sent out as multicasts. Many implementations cannot
receive these multicasts; ensure end-host ability before
using this command.
(Optional) Sets the IRDP period for which advertisements are valid.
The default is three times the maxadvertinterval value. It must be
greater than maxadvertinterval and cannot be greater than 9000
seconds. If you change the maxadvertinterval value, this value
also changes.
(Optional) Sets the IRDP maximum interval between
advertisements. The default is 600 seconds.
Example:
Switch(config-if)# ip irdp
maxadvertinterval 650
Step 8
ip irdp minadvertinterval seconds
Example:
(Optional) Sets the IRDP minimum interval between advertisements.
The default is 0.75 times the maxadvertinterval. If you change
the maxadvertinterval, this value changes to the new default (0.75
of maxadvertinterval).
Switch(config-if)# ip irdp
minadvertinterval 500
Step 9
ip irdp preference number
Example:
(Optional) Sets a device IRDP preference level. The allowed range
is –231 to 231. The default is 0. A higher value increases the router
preference level.
Switch(config-if)# ip irdp preference 2
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Configuring Broadcast Packet Handling
Step 10
Command or Action
Purpose
ip irdp address address [number]
(Optional) Specifies an IRDP address and preference to
proxy-advertise.
Example:
Switch(config-if)# ip irdp address
10.1.10.10
Step 11
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 12
show ip irdp
Verifies settings by displaying IRDP values.
Example:
Switch# show ip irdp
Step 13
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config
startup-config
Configuring Broadcast Packet Handling
Perform the tasks in these sections to enable these schemes:
• Enabling Directed Broadcast-to-Physical Broadcast Translation
• Forwarding UDP Broadcast Packets and Protocols
• Establishing an IP Broadcast Address
• Flooding IP Broadcasts
Broadcast Packet Handling
After configuring an IP interface address, you can enable routing and configure one or more routing protocols,
or you can configure the way the Switch responds to network broadcasts. A broadcast is a data packet destined
for all hosts on a physical network. The Switch supports two kinds of broadcasting:
• A directed broadcast packet is sent to a specific network or series of networks. A directed broadcast
address includes the network or subnet fields.
• A flooded broadcast packet is sent to every network.
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Configuring IP Unicast Routing
Configuring Broadcast Packet Handling
Note
You can also limit broadcast, unicast, and multicast traffic on Layer 2 interfaces by
using the storm-control interface configuration command to set traffic suppression
levels.
Routers provide some protection from broadcast storms by limiting their extent to the local cable. Bridges
(including intelligent bridges), because they are Layer 2 devices, forward broadcasts to all network segments,
thus propagating broadcast storms. The best solution to the broadcast storm problem is to use a single broadcast
address scheme on a network. In most modern IP implementations, you can set the address to be used as the
broadcast address. Many implementations, including the one in the Switch, support several addressing schemes
for forwarding broadcast messages.
Enabling Directed Broadcast-to-Physical Broadcast Translation
By default, IP directed broadcasts are dropped; they are not forwarded. Dropping IP-directed broadcasts makes
routers less susceptible to denial-of-service attacks.
You can enable forwarding of IP-directed broadcasts on an interface where the broadcast becomes a physical
(MAC-layer) broadcast. Only those protocols configured by using the ip forward-protocol global configuration
command are forwarded.
You can specify an access list to control which broadcasts are forwarded. When an access list is specified,
only those IP packets permitted by the access list are eligible to be translated from directed broadcasts to
physical broadcasts. For more information on access lists, see the “Information about Network Security with
ACLs" section in the Security Configuration Guide.
Use the no ip directed-broadcast interface configuration command to disable translation of directed broadcast
to physical broadcasts. Use the no ip forward-protocol global configuration command to remove a protocol
or port.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if
prompted.
Example:
Switch> enable
Step 2
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
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Configuring IP Unicast Routing
Configuring Broadcast Packet Handling
Step 3
Command or Action
Purpose
interface interface-id
Enters interface configuration mode, and specifies the interface
to configure.
Example:
Switch(config)# interface gigabitethernet
1/0/2
Step 4
ip directed-broadcast [access-list-number]
Example:
Enables directed broadcast-to-physical broadcast translation on
the interface. You can include an access list to control which
broadcasts are forwarded. When an access list, only IP packets
permitted by the access list can be translated.
Switch(config-if)# ip directed-broadcast
103
Step 5
exit
Returns to global configuration mode.
Example:
Switch(config-if)# exit
Step 6
ip forward-protocol {udp [port] | nd | sdns}
Example:
Switch(config)# ip forward-protocol nd
Specifies which protocols and ports the router forwards when
forwarding broadcast packets.
• udp—Forward UPD datagrams.
port: (Optional) Destination port that controls which UDP
services are forwarded.
• nd—Forward ND datagrams.
• sdns—Forward SDNS datagrams
Step 7
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 8
show ip interface [interface-id]
Verifies the configuration on the interface or all interfaces
Example:
Switch# show ip interface
Step 9
show running-config
Verifies your entries.
Example:
Switch# show running-config
Step 10
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
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Configuring IP Unicast Routing
Configuring Broadcast Packet Handling
Command or Action
Purpose
UDP Broadcast Packets and Protocols
User Datagram Protocol (UDP) is an IP host-to-host layer protocol, as is TCP. UDP provides a low-overhead,
connectionless session between two end systems and does not provide for acknowledgment of received
datagrams. Network hosts occasionally use UDP broadcasts to find address, configuration, and name
information. If such a host is on a network segment that does not include a server, UDP broadcasts are normally
not forwarded. You can remedy this situation by configuring an interface on a router to forward certain classes
of broadcasts to a helper address. You can use more than one helper address per interface.
You can specify a UDP destination port to control which UDP services are forwarded. You can specify multiple
UDP protocols. You can also specify the Network Disk (ND) protocol, which is used by older diskless Sun
workstations and the network security protocol SDNS.
By default, both UDP and ND forwarding are enabled if a helper address has been defined for an interface.
The description for the ip forward-protocol interface configuration command in the Cisco IOS IP Command
Reference, Volume 1 of 3: Addressing and Services lists the ports that are forwarded by default if you do not
specify any UDP ports.
Forwarding UDP Broadcast Packets and Protocols
If you do not specify any UDP ports when you configure the forwarding of UDP broadcasts, you are configuring
the router to act as a BOOTP forwarding agent. BOOTP packets carry DHCP information.
Use the no ip helper-address interface configuration command to disable the forwarding of broadcast packets
to specific addresses. Use the no ip forward-protocol global configuration command to remove a protocol
or port.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if
prompted.
Example:
Switch> enable
Step 2
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
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Configuring IP Unicast Routing
Configuring Broadcast Packet Handling
Step 3
Command or Action
Purpose
interface interface-id
Enters interface configuration mode, and specifies the
Layer 3 interface to configure.
Example:
Switch(config)# interface gigabitethernet 1/0/1
Step 4
ip helper-address address
Example:
Enables forwarding and specifies the destination address
for forwarding UDP broadcast packets, including
BOOTP.
Switch(config-if)# ip helper address 10.1.10.1
Step 5
exit
Returns to global configuration mode.
Example:
Switch(config-if)# exit
Step 6
ip forward-protocol {udp [port] | nd | sdns}
Specifies which protocols the router forwards when
forwarding broadcast packets.
Example:
Switch(config)# ip forward-protocol sdns
Step 7
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 8
show ip interface [interface-id]
Verifies the configuration on the interface or all
interfaces.
Example:
Switch# show ip interface gigabitethernet 1/0/1
Step 9
show running-config
Verifies your entries.
Example:
Switch# show running-config
Step 10
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
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Configuring IP Unicast Routing
Configuring Broadcast Packet Handling
Establishing an IP Broadcast Address
The most popular IP broadcast address (and the default) is an address consisting of all ones (255.255.255.255).
However, the Switch can be configured to generate any form of IP broadcast address.
To restore the default IP broadcast address, use the no ip broadcast-address interface configuration command.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if
prompted.
Example:
Switch> enable
Step 2
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
Step 3
interface interface-id
Enters interface configuration mode, and specifies the
interface to configure.
Example:
Switch(config)# interface gigabitethernet 1/0/1
Step 4
ip broadcast-address ip-address
Enters a broadcast address different from the default, for
example 128.1.255.255.
Example:
Switch(config-if)# ip broadcast-address
128.1.255.255
Step 5
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 6
show ip interface [interface-id]
Verifies the broadcast address on the interface or all
interfaces.
Example:
Switch# show ip interface
Step 7
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
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Configuring IP Unicast Routing
Configuring Broadcast Packet Handling
IP Broadcast Flooding
You can allow IP broadcasts to be flooded throughout your internetwork in a controlled fashion by using the
database created by the bridging STP. Using this feature also prevents loops. To support this capability,
bridging must be configured on each interface that is to participate in the flooding. If bridging is not configured
on an interface, it still can receive broadcasts. However, the interface never forwards broadcasts it receives,
and the router never uses that interface to send broadcasts received on a different interface.
Packets that are forwarded to a single network address using the IP helper-address mechanism can be flooded.
Only one copy of the packet is sent on each network segment.
To be considered for flooding, packets must meet these criteria. (Note that these are the same conditions used
to consider packet forwarding using IP helper addresses.)
• The packet must be a MAC-level broadcast.
• The packet must be an IP-level broadcast.
• The packet must be a TFTP, DNS, Time, NetBIOS, ND, or BOOTP packet, or a UDP specified by the
ip forward-protocol udp global configuration command.
• The time-to-live (TTL) value of the packet must be at least two.
A flooded UDP datagram is given the destination address specified with the ip broadcast-address interface
configuration command on the output interface. The destination address can be set to any address. Thus, the
destination address might change as the datagram propagates through the network. The source address is never
changed. The TTL value is decremented.
When a flooded UDP datagram is sent out an interface (and the destination address possibly changed), the
datagram is handed to the normal IP output routines and is, therefore, subject to access lists, if they are present
on the output interface.
Use the no ip forward-protocol spanning-tree global configuration command to disable the flooding of IP
broadcasts.
In the Switch, the majority of packets are forwarded in hardware; most packets do not go through the Switch
CPU. For those packets that do go to the CPU, you can speed up spanning tree-based UDP flooding by a
factor of about four to five times by using turbo-flooding. This feature is supported over Ethernet interfaces
configured for ARP encapsulation.
To disable this feature, use the no ip forward-protocol turbo-flood global configuration command
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Configuring IP Unicast Routing
Configuring Broadcast Packet Handling
Flooding IP Broadcasts
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password
if prompted.
Example:
Switch> enable
Step 2
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
Step 3
ip forward-protocol spanning-tree
Uses the bridging spanning-tree database to flood
UDP datagrams.
Example:
Switch(config)# ip forward-protocol spanning-tree
Step 4
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 5
show running-config
Verifies your entries.
Example:
Switch# show running-config
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration
file.
Example:
Switch# copy running-config startup-config
Step 7
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
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Configuring IP Unicast Routing
Monitoring and Maintaining IP Addressing
Step 8
Command or Action
Purpose
ip forward-protocol turbo-flood
Uses the spanning-tree database to speed up flooding
of UDP datagrams.
Example:
Switch(config)# ip forward-protocol turbo-flood
Step 9
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 10
Verifies your entries.
show running-config
Example:
Switch# show running-config
Step 11
(Optional) Saves your entries in the configuration
file.
copy running-config startup-config
Example:
Switch# copy running-config startup-config
Monitoring and Maintaining IP Addressing
When the contents of a particular cache, table, or database have become or are suspected to be invalid, you
can remove all its contents by using the clear privileged EXEC commands. The Table lists the commands for
clearing contents.
Table 2: Commands to Clear Caches, Tables, and Databases
clear arp-cache
Clears the IP ARP cache and the fast-switching cache.
clear host {name | *}
Removes one or all entries from the hostname and the address
cache.
clear ip route {network [mask] | *}
Removes one or more routes from the IP routing table.
You can display specific statistics, such as the contents of IP routing tables, caches, and databases; the
reachability of nodes; and the routing path that packets are taking through the network. The Table lists the
privileged EXEC commands for displaying IP statistics.
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How to Configure IP Unicast Routing
Table 3: Commands to Display Caches, Tables, and Databases
show arp
Displays the entries in the ARP table.
show hosts
Displays the default domain name, style of lookup service, name
server hosts, and the cached list of hostnames and addresses.
show ip aliases
Displays IP addresses mapped to TCP ports (aliases).
show ip arp
Displays the IP ARP cache.
show ip interface [interface-id]
Displays the IP status of interfaces.
show ip irdp
Displays IRDP values.
show ip masks address
Displays the masks used for network addresses and the number of
subnets using each mask.
show ip redirects
Displays the address of a default gateway.
show ip route [address [mask]] |
[protocol]
Displays the current state of the routing table.
show ip route summary
Displays the current state of the routing table in summary form.
How to Configure IP Unicast Routing
Enabling IP Unicast Routing
By default, the Switch is in Layer 2 switching mode and IP routing is disabled. To use the Layer 3 capabilities
of the Switch, you must enable IP routing.
Use the no ip routing global configuration command to disable routing.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if
prompted.
Example:
Switch> enable
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Configuring IP Unicast Routing
Example of Enabling IP Routing
Step 2
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 3
ip routing
Enables IP routing.
Example:
Switch(config)# ip routing
Step 4
router ip_routing_protocol
Example:
Switch(config)# router rip
Step 5
Specifies an IP routing protocol. This step might include other
commands, such as specifying the networks to route with the
network (RIP) router configuration command. For information
on specific protocols, see sections later in this chapter and to
the Cisco IOS IP Configuration Guide.
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 6
show running-config
Verifies your entries.
Example:
Switch# show running-config
Step 7
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Example of Enabling IP Routing
This example shows how to enable IP routingusing RIP as the routing protocol :
Switch# configure terminal
Enter configuration commands, one per line.
Switch(config)# ip routing
End with CNTL/Z.
Switch(config-router)# end
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Configuring IP Unicast Routing
Information About RIP
Information About RIP
The Routing Information Protocol (RIP) is an interior gateway protocol (IGP) created for use in small,
homogeneous networks. It is a distance-vector routing protocol that uses broadcast User Datagram Protocol
(UDP) data packets to exchange routing information. The protocol is documented in RFC 1058. You can find
detailed information about RIP in IP Routing Fundamentals, published by Cisco Press.
Note
RIP is supported in the .
Note
RIP is the only routing protocol supported by the IP base feature set; other routing protocols require the
switch or stack master to be running the IP services feature set.
Using RIP, the Switch sends routing information updates (advertisements) every 30 seconds. If a router does
not receive an update from another router for 180 seconds or more, it marks the routes served by that router
as unusable. If there is still no update after 240 seconds, the router removes all routing table entries for the
non-updating router.
RIP uses hop counts to rate the value of different routes. The hop count is the number of routers that can be
traversed in a route. A directly connected network has a hop count of zero; a network with a hop count of 16
is unreachable. This small range (0 to 15) makes RIP unsuitable for large networks.
If the router has a default network path, RIP advertises a route that links the router to the pseudonetwork
0.0.0.0. The 0.0.0.0 network does not exist; it is treated by RIP as a network to implement the default routing
feature. The Switch advertises the default network if a default was learned by RIP or if the router has a gateway
of last resort and RIP is configured with a default metric. RIP sends updates to the interfaces in specified
networks. If an interface’s network is not specified, it is not advertised in any RIP update.
How to Configure RIP
Default RIP Configuration
Table 4: Default RIP Configuration
Feature
Default Setting
Auto summary
Enabled.
Default-information
originate
Disabled.
Default metric
Built-in; automatic metric translations.
IP RIP authentication
key-chain
No authentication.
Authentication mode: clear text.
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Configuring IP Unicast Routing
Configuring Basic RIP Parameters
Feature
Default Setting
IP RIP triggered
Disabled
IP RIP receive version
According to the version router configuration command.
IP RIP send version
According to the version router configuration command.
IP RIP triggered
According to the version router configuration command.
IP split horizon
Varies with media.
Neighbor
None defined.
Network
None specified.
Offset list
Disabled.
Output delay
0 milliseconds.
Timers basic
• Update: 30 seconds.
• Invalid: 180 seconds.
• Hold-down: 180 seconds.
• Flush: 240 seconds.
Validate-update-source
Enabled.
Version
Receives RIP Version 1 and 2 packets; sends Version 1 packets.
Configuring Basic RIP Parameters
To configure RIP, you enable RIP routing for a network and optionally configure other parameters. On the
Switch, RIP configuration commands are ignored until you configure the network number.
To turn off the RIP routing process, use the no router rip global configuration command.
To display the parameters and current state of the active routing protocol process, use the show ip protocols
privileged EXEC command. Use the show ip rip database privileged EXEC command to display summary
address entries in the RIP database.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password if prompted.
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Configuring IP Unicast Routing
Configuring Basic RIP Parameters
Command or Action
Purpose
Example:
Switch> enable
Step 2
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
Step 3
Enables IP routing. (Required only if IP routing is disabled.)
ip routing
Example:
Switch(config)# ip routing
Step 4
Enables a RIP routing process, and enter router configuration mode.
router rip
Example:
Switch(config)# router rip
Step 5
Step 6
network network number
Example:
Associates a network with a RIP routing process. You can specify multiple
network commands. RIP routing updates are sent and received through
interfaces only on these networks.
Switch(config)# network 12
Note
neighbor ip-address
You must configure a network number for the RIP commands to
take effect.
(Optional) Defines a neighboring router with which to exchange routing
information. This step allows routing updates from RIP (normally a
broadcast protocol) to reach nonbroadcast networks.
Example:
Switch(config)# neighbor 10.2.5.1
Step 7
offset-list [access-list number | name] {in (Optional) Applies an offset list to routing metrics to increase incoming
and outgoing metrics to routes learned through RIP. You can limit the offset
| out} offset [type number]
list with an access list or an interface.
Example:
Switch(config)# offset-list 103 in
10
Step 8
timers basic update invalid holddown
flush
(Optional) Adjusts routing protocol timers. Valid ranges for all timers are
0 to 4294967295 seconds.
• update—The time between sending routing updates. The default is
30 seconds.
Example:
Switch(config)# timers basic 45 360
400 300
• invalid—The timer after which a route is declared invalid. The default
is 180 seconds.
• holddown—The time before a route is removed from the routing table.
The default is 180 seconds.
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Configuring Basic RIP Parameters
Command or Action
Purpose
• flush—The amount of time for which routing updates are postponed.
The default is 240 seconds.
Step 9
version {1 | 2}
Example:
Switch(config)# version 2
Step 10
no auto summary
Example:
(Optional) Configures the switch to receive and send only RIP Version 1
or RIP Version 2 packets. By default, the switch receives Version 1 and 2
but sends only Version 1. You can also use the interface commands ip rip
{send | receive} version 1 | 2 | 1 2} to control what versions are used for
sending and receiving on interfaces.
(Optional) Disables automatic summarization. By default, the switch
summarizes subprefixes when crossing classful network boundaries. Disable
summarization (RIP Version 2 only) to advertise subnet and host routing
information to classful network boundaries.
Switch(config)# no auto summary
Step 11
no validate-update-source
Example:
Switch(config)# no
validdate-update-source
Step 12
output-delay delay
Example:
(Optional) Disables validation of the source IP address of incoming RIP
routing updates. By default, the switch validates the source IP address of
incoming RIP routing updates and discards the update if the source address
is not valid. Under normal circumstances, disabling this feature is not
recommended. However, if you have a router that is off-network and you
want to receive its updates, you can use this command.
(Optional) Adds interpacket delay for RIP updates sent. By default, packets
in a multiple-packet RIP update have no delay added between packets. If
you are sending packets to a lower-speed device, you can add an interpacket
delay in the range of 8 to 50 milliseconds.
Switch(config)# output-delay 8
Step 13
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 14
show ip protocols
Verifies your entries.
Example:
Switch# show ip protocols
Step 15
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config
startup-config
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Configuring IP Unicast Routing
Configuring RIP Authentication
Configuring RIP Authentication
RIP Version 1 does not support authentication. If you are sending and receiving RIP Version 2 packets, you
can enable RIP authentication on an interface. The key chain specifies the set of keys that can be used on the
interface. If a key chain is not configured, no authentication is performed, not even the default.
The Switch supports two modes of authentication on interfaces for which RIP authentication is enabled: plain
text and MD5. The default is plain text.
To restore clear text authentication, use the no ip rip authentication mode interface configuration command.
To prevent authentication, use the no ip rip authentication key-chain interface configuration command.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password
if prompted.
Example:
Switch> enable
Step 2
Enters the global configuration mode.
configure terminal
Example:
Switch# configure terminal
Step 3
interface interface-id
Enters interface configuration mode, and specifies the
interface to configure.
Example:
Switch(config)# interface gigabitethernet 1/0/1
Step 4
ip rip authentication key-chain name-of-chain
Enables RIP authentication.
Example:
Switch(config-if)# ip rip authentication key-chain
trees
Step 5
ip rip authentication mode {text | md5}
Example:
Configures the interface to use plain text
authentication (the default) or MD5 digest
authentication.
Switch(config-if)# ip rip authentication mode md5
Step 6
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
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Configuring IP Unicast Routing
Summary Addresses and Split Horizon
Step 7
Command or Action
Purpose
show running-config
Verifies your entries.
Example:
Switch# show running-config
Step 8
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Summary Addresses and Split Horizon
Routers connected to broadcast-type IP networks and using distance-vector routing protocols normally use
the split-horizon mechanism to reduce the possibility of routing loops. Split horizon blocks information about
routes from being advertised by a router on any interface from which that information originated. This feature
usually optimizes communication among multiple routers, especially when links are broken.
Configuring Summary Addresses and Split Horizon
Note
In general, disabling split horizon is not recommended unless you are certain that your application requires
it to properly advertise routes.
If you want to configure an interface running RIP to advertise a summarized local IP address pool on a network
access server for dial-up clients, use the ip summary-address rip interface configuration command.
Note
If split horizon is enabled, neither autosummary nor interface IP summary addresses are advertised.
To disable IP summarization, use the no ip summary-address rip router configuration command.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your
password if prompted.
Example:
Switch> enable
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Configuring IP Unicast Routing
Configuring Summary Addresses and Split Horizon
Step 2
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 3
interface interface-id
Enters interface configuration mode, and specifies
the Layer 3 interface to configure.
Example:
Switch(config)# interface gigabitethernet 1/0/1
Step 4
ip address ip-address subnet-mask
Configures the IP address and IP subnet.
Example:
Switch(config-if)# ip address 10.1.1.10
255.255.255.0
Step 5
ip summary-address rip ip address ip-network mask
Configures the IP address to be summarized and the
IP network mask.
Example:
Switch(config-if)# ip summary-address rip ip address
10.1.1.30 255.255.255.0
Step 6
Disables split horizon on the interface.
no ip split horizon
Example:
Switch(config-if)# no ip split horizon
Step 7
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 8
show ip interface interface-id
Verifies your entries.
Example:
Switch# show ip interface gigabitethernet 1/0/1
Step 9
copy running-config startup-config
(Optional) Saves your entries in the configuration
file.
Example:
Switch# copy running-config startup-config
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Configuring IP Unicast Routing
Configuring Split Horizon
Configuring Split Horizon
Routers connected to broadcast-type IP networks and using distance-vector routing protocols normally use
the split-horizon mechanism to reduce the possibility of routing loops. Split horizon blocks information about
routes from being advertised by a router on any interface from which that information originated. This feature
can optimize communication among multiple routers, especially when links are broken.
Note
In general, we do not recommend disabling split horizon unless you are certain that your application
requires it to properly advertise routes.
To enable the split horizon mechanism, use the ip split-horizon interface configuration command.
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your
password if prompted.
Example:
Switch> enable
Step 2
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 3
interface interface-id
Enters interface configuration mode, and specifies
the interface to configure.
Example:
Switch(config)# interface gigabitethernet 1/0/1
Step 4
ip address ip-address subnet-mask
Configures the IP address and IP subnet.
Example:
Switch(config-if)# ip address 10.1.1.10
255.255.255.0
Step 5
no ip split-horizon
Disables split horizon on the interface.
Example:
Switch(config-if)# no ip split-horizon
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Configuring IP Unicast Routing
Configuration Example for Summary Addresses and Split Horizon
Step 6
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 7
show ip interface interface-id
Verifies your entries.
Example:
Switch# show ip interface gigabitethernet 1/0/1
Step 8
copy running-config startup-config
(Optional) Saves your entries in the configuration
file.
Example:
Switch# copy running-config startup-config
Configuration Example for Summary Addresses and Split Horizon
In this example, the major net is 10.0.0.0. The summary address 10.2.0.0 overrides the autosummary address
of 10.0.0.0 so that 10.2.0.0 is advertised out interface Gigabit Ethernet port 2, and 10.0.0.0 is not advertised.
In the example, if the interface is still in Layer 2 mode (the default), you must enter a no switchport interface
configuration command before entering the ip address interface configuration command.
Note
If split horizon is enabled, neither autosummary nor interface summary addresses (those configured with
the ip summary-address rip router configuration command) are advertised.
Switch(config)# router rip
Switch(config-router)# interface gigabitethernet1/0/2
Switch(config-if)# ip address 10.1.5.1 255.255.255.0
Switch(config-if)# ip summary-address rip 10.2.0.0 255.255.0.0
Switch(config-if)# no ip split-horizon
Switch(config-if)# exit
Switch(config)# router rip
Switch(config-router)# network 10.0.0.0
Switch(config-router)# neighbor 2.2.2.2 peer-group mygroup
Switch(config-router)# end
Information About OSPF
OSPF is an Interior Gateway Protocol (IGP) designed expressly for IP networks, supporting IP subnetting
and tagging of externally derived routing information. OSPF also allows packet authentication and uses IP
multicast when sending and receiving packets. The Cisco implementation supports RFC 1253, OSPF
management information base (MIB).
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Configuring IP Unicast Routing
How to Configure OSPF
Note
OSPF classifies different media into broadcast, nonbroadcast, and point-to-point networks. The switch
supports broadcast (Ethernet, Token Ring, and FDDI) and point-to-point networks (Ethernet interfaces
configured as point-to-point links).
The Cisco implementation conforms to the OSPF Version 2 specifications with these key features:
• Definition of stub areas is supported.
• Routes learned through any IP routing protocol can be redistributed into another IP routing protocol. At
the intradomain level, this means that OSPF can import routes learned through EIGRP and RIP. OSPF
routes can also be exported into RIP.
• Plain text and MD5 authentication among neighboring routers within an area is supported.
• Configurable routing interface parameters include interface output cost, retransmission interval, interface
transmit delay, router priority, router dead and hello intervals, and authentication key.
• Virtual links are supported.
• Not-so-stubby-areas (NSSAs) per RFC 1587are supported.
OSPF typically requires coordination among many internal routers, area border routers (ABRs) connected to
multiple areas, and autonomous system boundary routers (ASBRs). The minimum configuration would use
all default parameter values, no authentication, and interfaces assigned to areas. If you customize your
environment, you must ensure coordinated configuration of all routers.
How to Configure OSPF
Default OSPF Configuration
Table 5: Default OSPF Configuration
Feature
Default Setting
Interface parameters
Cost: No default cost predefined
Retransmit interval: 5 seconds.
Transmit delay: 1 second.
Priority: 1.
Hello interval: 10 seconds.
Dead interval: 4 times the hello interval.
No authentication.
No password specified.
MD5 authentication disabled.
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How to Configure OSPF
Feature
Default Setting
Area
Authentication type: 0 (no authentication).
Default cost: 1.
Range: Disabled.
Stub: No stub area defined.
NSSA: No NSSA area defined.
Auto cost
100 Mb/s.
Default-information originate
Disabled. When enabled, the default metric setting is 10, and the external
route type default is Type 2.
Default metric
Built-in, automatic metric translation, as appropriate for each routing
protocol.
Distance OSPF
dist1 (all routes within an area): 110.
dist2 (all routes from one area to another): 110.
dist3 (routes from other routing domains): 110.
OSPF database filter
Disabled. All outgoing link-state advertisements (LSAs) are flooded to the
interface.
IP OSPF name lookup
Disabled.
Log adjacency changes
Enabled.
Neighbor
None specified.
Neighbor database filter
Disabled. All outgoing LSAs are flooded to the neighbor.
Network area
Disabled.
Nonstop Forwarding (NSF)
awareness
Enabled. Allows Layer 3 Switch to continue forwarding packets from a
neighboring NSF-capable router during hardware or software changes.
NSF capability
Disabled.
Note
The Switch stack supports OSPF NSF-capable routing for
IPv4.
Router ID
No OSPF routing process defined.
Summary address
Disabled.
Timers LSA group pacing
240 seconds.
Timers shortest path first (spf) spf delay: 5 seconds.; spf-holdtime: 10 seconds.
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Configuring IP Unicast Routing
How to Configure OSPF
Feature
Default Setting
Virtual link
No area ID or router ID defined.
Hello interval: 10 seconds.
Retransmit interval: 5 seconds.
Transmit delay: 1 second.
Dead interval: 40 seconds.
Authentication key: no key predefined.
Message-digest key (MD5): no key predefined.
OSPF for Routed Access
With Cisco IOS Release 12.2(55)SE, the IP Base image supports OSPF for routed access. The IP services
image is required if you need multiple OSPFv2 and OSPFv3 instances without route restrictions. Additionally,
the IP services image is required to enable the multi-VRF-CE feature.
OSPF for Routed Access is specifically designed so that you can extend Layer 3 routing capabilities to the
wiring closet.
Note
OSPF for Routed Access supports only one OSPFv2 and one OSPFv3 instance with a combined total of
200 dynamically learned routes. The IP Base image provides OSPF for routed access.
However, these restrictions are not enforced in this release.
With the typical topology (hub and spoke) in a campus environment, where the wiring closets (spokes) are
connected to the distribution switch (hub) that forwards all nonlocal traffic to the distribution layer, the wiring
closet Switch need not hold a complete routing table. A best practice design, where the distribution Switch
sends a default route to the wiring closet Switch to reach interarea and external routes (OSPF stub or totally
stub area configuration) should be used when OSPF for Routed Access is used in the wiring closet.
For more details, see the “High Availability Campus Network Design—Routed Access Layer using EIGRP
or OSPF” document.
OSPF Nonstop Forwarding
The Switch or switch stack supports two levels of nonstop forwarding (NSF):
• OSPF NSF Awareness, on page 44
• OSPF NSF Capability, on page 45
OSPF NSF Awareness
The IP-services feature set supports OSPF NSF Awareness supported for IPv4. When the neighboring router
is NSF-capable, the Layer 3 Switch continues to forward packets from the neighboring router during the
interval between the primary Route Processor (RP) in a router crashing and the backup RP taking over, or
while the primary RP is manually reloaded for a non-disruptive software upgrade.
This feature cannot be disabled.
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Configuring IP Unicast Routing
How to Configure OSPF
OSPF NSF Capability
The IP services feature set supports the OSPFv2 NSF IETF format in addition to the OSPFv2 NSF Cisco
format that is supported in earlier releases. For information about this feature, see : NSF—OSPF (RFC 3623
OSPF Graceful Restart).
The IP-services feature set also supports OSPF NSF-capable routing for IPv4 for better convergence and
lower traffic loss following a stack master change. When a stack master change occurs in an OSPF NSF-capable
stack, the new stack master must do two things to resynchronize its link-state database with its OSPF neighbors:
• Release the available OSPF neighbors on the network without resetting the neighbor relationship.
• Reacquire the contents of the link-state database for the network.
After a stack master change, the new master sends an OSPF NSF signal to neighboring NSF-aware devices.
A device recognizes this signal to mean that it should not reset the neighbor relationship with the stack. As
the NSF-capable stack master receives signals from other routes on the network, it begins to rebuild its neighbor
list.
When the neighbor relationships are reestablished, the NSF-capable stack master resynchronizes its database
with its NSF-aware neighbors, and routing information is exchanged between the OSPF neighbors. The new
stack master uses this routing information to remove stale routes, to update the routing information database
(RIB), and to update the forwarding information base (FIB) with the new information. The OSPF protocols
then fully converge.
Note
OSPF NSF requires that all neighbor networking devices be NSF-aware. If an NSF-capable router discovers
non-NSF aware neighbors on a network segment, it disables NSF capabilities for that segment. Other
network segments where all devices are NSF-aware or NSF-capable continue to provide NSF capabilities.
Use the nsf OSPF routing configuration command to enable OSPF NSF routing. Use the show ip ospf
privileged EXEC command to verify that it is enabled.
For more information, see Cisco Nonstop Forwarding: http://www.cisco.com/en/US/docs/ios/ha/configuration/
guide/ha-nonstp_fwdg.html
Note
NSF is not supported on interfaces configured for Hot Standby Router Protocol (HSRP).
Configuring Basic OSPF Parameters
To enable OSPF, create an OSPF routing process, specify the range of IP addresses to associate with the
routing process, and assign area IDs to be associated with that range. For switches running the IP services
image, you can configure either the Cisco OSPFv2 NSF format or the IETF OSPFv2 NSF format.
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How to Configure OSPF
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router ospf process-id
Example:
Enables OSPF routing, and enter router configuration mode. The process
ID is an internally used identification parameter that is locally assigned
and can be any positive integer. Each OSPF routing process has a unique
value.
Switch(config)# router ospf 15
Note
Step 3
nsf cisco [enforce global]
Example:
Switch(config)# nsf cisco enforce
global
Step 4
nsf ietf [restart-interval seconds]
Example:
Switch(config)# nsf ietf
restart-interval 60
Step 5
OSPF for Routed Access supports only one OSPFv2 and one
OSPFv3 instance with a maximum number of 200 dynamically
learned routes.
(Optional) Enables Cisco NSF operations for OSPF. The enforce global
keyword cancels NSF restart when non-NSF-aware neighboring
networking devices are detected.
Note
Enter the command in Step 3 or Step 4, and go to Step
5.
(Optional) Enables IETF NSF operations for OSPF. The restart-interval
keyword specifies the length of the graceful restart interval, in seconds.
The range is from 1 to 1800. The default is 120.
Note
Enter the command in Step 3 or Step 4, and go to Step
5.
network address wildcard-mask area area-id Define an interface on which OSPF runs and the area ID for that
interface. You can use the wildcard-mask to use a single command to
define one or more multiple interfaces to be associated with a specific
Example:
OSPF area. The area ID can be a decimal value or an IP address.
Switch(config)# network 10.1.1.1
255.240.0.0 area 20
Step 6
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 7
show ip protocols
Verifies your entries.
Example:
Switch# show ip protocols
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How to Configure OSPF
Step 8
Command or Action
Purpose
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config
startup-config
Example: Configuring Basic OSPF Parameters
This example shows how to configure an OSPF routing process and assign it a process number of 109:
Switch(config)# router ospf 109
Switch(config-router)# network 131.108.0.0 255.255.255.0 area 24
Configuring OSPF Interfaces
You can use the ip ospf interface configuration commands to modify interface-specific OSPF parameters.
You are not required to modify any of these parameters, but some interface parameters (hello interval, dead
interval, and authentication key) must be consistent across all routers in an attached network. If you modify
these parameters, be sure all routers in the network have compatible values.
Note
The ip ospf interface configuration commands are all optional.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
interface interface-id
Enters interface configuration mode, and specifies the Layer 3
interface to configure.
Example:
Switch(config)# interface gigabitethernet
1/0/1
Step 3
ip ospf cost
(Optional) Explicitly specifies the cost of sending a packet on the
interface.
Example:
Switch(config-if)# ip ospf 8
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Step 4
Command or Action
Purpose
ip ospf retransmit-interval seconds
(Optional) Specifies the number of seconds between link state
advertisement transmissions. The range is 1 to 65535 seconds. The
default is 5 seconds.
Example:
Switch(config-if)# ip ospf
transmit-interval 10
Step 5
ip ospf transmit-delay seconds
Example:
(Optional) Sets the estimated number of seconds to wait before
sending a link state update packet. The range is 1 to 65535 seconds.
The default is 1 second.
Switch(config-if)# ip ospf transmit-delay
2
Step 6
ip ospf priority number
(Optional) Sets priority to help find the OSPF designated router for
a network. The range is from 0 to 255. The default is 1.
Example:
Switch(config-if)# ip ospf priority 5
Step 7
ip ospf hello-interval seconds
Example:
(Optional) Sets the number of seconds between hello packets sent
on an OSPF interface. The value must be the same for all nodes on
a network. The range is 1 to 65535 seconds. The default is 10
seconds.
Switch(config-if)# ip ospf hello-interval
12
Step 8
ip ospf dead-interval seconds
Example:
(Optional) Sets the number of seconds after the last device hello
packet was seen before its neighbors declare the OSPF router to be
down. The value must be the same for all nodes on a network. The
range is 1 to 65535 seconds. The default is 4 times the hello interval.
Switch(config-if)# ip ospf dead-interval
8
Step 9
ip ospf authentication-key key
Example:
Switch(config-if)# ip ospf
authentication-key password
Step 10
ip ospf message digest-key keyid md5 key
Example:
Switch(config-if)# ip ospf message
digest-key 16 md5 your1pass
Step 11
ip ospf database-filter all out
Example:
(Optional) Assign a password to be used by neighboring OSPF
routers. The password can be any string of keyboard-entered
characters up to 8 bytes in length. All neighboring routers on the
same network must have the same password to exchange OSPF
information.
(Optional) Enables MDS authentication.
• keyid—An identifier from 1 to 255.
• key—An alphanumeric password of up to 16 bytes.
(Optional) Block flooding of OSPF LSA packets to the interface.
By default, OSPF floods new LSAs over all interfaces in the same
area, except the interface on which the LSA arrives.
Switch(config-if)# ip ospf
database-filter all out
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How to Configure OSPF
Step 12
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 13
show ip ospf interface [interface-name]
Displays OSPF-related interface information.
Example:
Switch# show ip ospf interface
Step 14
show ip ospf neighbor detail
Example:
Displays NSF awareness status of neighbor switch. The output
matches one of these examples:
• Options is 0x52
Switch# show ip ospf neighbor detail
LLS Options is 0x1 (LR)
When both of these lines appear, the neighbor switch is NSF
aware.
• Options is 0x42—This means the neighbor switch is not NSF
aware.
Step 15
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config
startup-config
Related Topics
Configuring Other OSPF Parameters, on page 52
OSPF Area Parameters
You can optionally configure several OSPF area parameters. These parameters include authentication for
password-based protection against unauthorized access to an area, stub areas, and not-so-stubby-areas (NSSAs).
Stub areas are areas into which information on external routes is not sent. Instead, the area border router (ABR)
generates a default external route into the stub area for destinations outside the autonomous system (AS). An
NSSA does not flood all LSAs from the core into the area, but can import AS external routes within the area
by redistribution.
Route summarization is the consolidation of advertised addresses into a single summary route to be advertised
by other areas. If network numbers are contiguous, you can use the area range router configuration command
to configure the ABR to advertise a summary route that covers all networks in the range.
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How to Configure OSPF
Configuring OSPF Area Parameters
Before You Begin
Note
The OSPF area router configuration commands are all optional.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router ospf process-id
Enables OSPF routing, and enter router configuration mode.
Example:
Switch(config)# router ospf 109
Step 3
area area-id authentication
Example:
(Optional) Allow password-based protection against unauthorized
access to the identified area. The identifier can be either a decimal
value or an IP address.
Switch(config-router)# area 1 authentication
Step 4
area area-id authentication message-digest
(Optional) Enables MD5 authentication on the area.
Example:
Switch(config-router)# area 1 authentication
message-digest
Step 5
area area-id stub [no-summary]
Example:
(Optional) Define an area as a stub area. The no-summary
keyword prevents an ABR from sending summary link
advertisements into the stub area.
Switch(config-router)# area 1 stub
Step 6
area area-id nssa [no-redistribution]
[default-information-originate] [no-summary]
Example:
Switch(config-router)# area 1 nssa
default-information-originate
(Optional) Defines an area as a not-so-stubby-area. Every router
within the same area must agree that the area is NSSA. Select
one of these keywords:
• no-redistribution—Select when the router is an NSSA
ABR and you want the redistribute command to import
routes into normal areas, but not into the NSSA.
• default-information-originate—Select on an ABR to allow
importing type 7 LSAs into the NSSA.
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How to Configure OSPF
Command or Action
Purpose
• no-redistribution—Select to not send summary LSAs into
the NSSA.
Step 7
area area-id range address mask
(Optional) Specifies an address range for which a single route is
advertised. Use this command only with area border routers.
Example:
Switch(config-router)# area 1 range
255.240.0.0
Step 8
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 9
show ip ospf [process-id]
Displays information about the OSPF routing process in general
or for a specific process ID to verify configuration.
Example:
Switch# show ip ospf
Step 10
show ip ospf [process-id [area-id]] database
Displays lists of information related to the OSPF database for a
specific router.
Example:
Switch# show ip osfp database
Step 11
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Other OSPF Parameters
You can optionally configure other OSPF parameters in router configuration mode.
• Route summarization: When redistributing routes from other protocols. Each route is advertised
individually in an external LSA. To help decrease the size of the OSPF link state database, you can use
the summary-address router configuration command to advertise a single router for all the redistributed
routes included in a specified network address and mask.
• Virtual links: In OSPF, all areas must be connected to a backbone area. You can establish a virtual link
in case of a backbone-continuity break by configuring two Area Border Routers as endpoints of a virtual
link. Configuration information includes the identity of the other virtual endpoint (the other ABR) and
the nonbackbone link that the two routers have in common (the transit area). Virtual links cannot be
configured through a stub area.
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• Default route: When you specifically configure redistribution of routes into an OSPF routing domain,
the route automatically becomes an autonomous system boundary router (ASBR). You can force the
ASBR to generate a default route into the OSPF routing domain.
• Domain Name Server (DNS) names for use in all OSPF show privileged EXEC command displays
makes it easier to identify a router than displaying it by router ID or neighbor ID.
• Default Metrics: OSPF calculates the OSPF metric for an interface according to the bandwidth of the
interface. The metric is calculated as ref-bw divided by bandwidth, where ref is 10 by default, and
bandwidth (bw) is specified by the bandwidth interface configuration command. For multiple links
with high bandwidth, you can specify a larger number to differentiate the cost on those links.
• Administrative distance is a rating of the trustworthiness of a routing information source, an integer
between 0 and 255, with a higher value meaning a lower trust rating. An administrative distance of 255
means the routing information source cannot be trusted at all and should be ignored. OSPF uses three
different administrative distances: routes within an area (interarea), routes to another area (interarea),
and routes from another routing domain learned through redistribution (external). You can change any
of the distance values.
• Passive interfaces: Because interfaces between two devices on an Ethernet represent only one network
segment, to prevent OSPF from sending hello packets for the sending interface, you must configure the
sending device to be a passive interface. Both devices can identify each other through the hello packet
for the receiving interface.
• Route calculation timers: You can configure the delay time between when OSPF receives a topology
change and when it starts the shortest path first (SPF) calculation and the hold time between two SPF
calculations.
• Log neighbor changes: You can configure the router to send a syslog message when an OSPF neighbor
state changes, providing a high-level view of changes in the router.
Related Topics
Information About Route Maps, on page 146
How to Configure a Route Map
How to Control Route Distribution, on page 150
Configuring Other OSPF Parameters
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
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Step 2
Command or Action
Purpose
router ospf process-id
Enables OSPF routing, and enter router configuration mode.
Example:
Switch(config)# router ospf 10
Step 3
summary-address address mask
Example:
(Optional) Specifies an address and IP subnet mask for
redistributed routes so that only one summary route is
advertised.
Switch(config)# summary-address 10.1.1.1
255.255.255.0
Step 4
area area-id virtual-link router-id [hello-interval
seconds] [retransmit-interval seconds] [trans]
[[authentication-key key] | message-digest-key keyid
md5 key]]
(Optional) Establishes a virtual link and set its parameters.
Example:
Switch(config)# area 2 virtual-link
192.168.255.1 hello-interval 5
Step 5
default-information originate [always] [metric
metric-value] [metric-type type-value] [route-map
map-name]
(Optional) Forces the ASBR to generate a default route into
the OSPF routing domain. Parameters are all optional.
Example:
Switch(config)# default-information originate
metric 100 metric-type 1
Step 6
(Optional) Configures DNS name lookup. The default is
disabled.
ip ospf name-lookup
Example:
Switch(config)# ip ospf name-lookup
Step 7
ip auto-cost reference-bandwidth ref-bw
Example:
(Optional) Specifies an address range for which a single
route will be advertised. Use this command only with area
border routers.
Switch(config)# ip auto-cost reference-bandwidth
5
Step 8
distance ospf {[inter-area dist1] [inter-area dist2]
[external dist3]}
(Optional) Changes the OSPF distance values. The default
distance for each type of route is 110. The range is 1 to 255.
Example:
Switch(config)# distance ospf inter-area 150
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Step 9
Command or Action
Purpose
passive-interface type number
(Optional) Suppresses the sending of hello packets through
the specified interface.
Example:
Switch(config)# passive-interface
gigabitethernet 1/0/6
Step 10
timers throttle spf spf-delay spf-holdtime spf-wait
Example:
Switch(config)# timers throttle spf 200 100 100
(Optional) Configures route calculation timers.
• spf-delay—Delay between receiving a change to SPF
calculation. The range is from 1 to 600000
miliseconds.
• spf-holdtime—Delay between first and second SPF
calculation. The range is form 1 to 600000 in
milliseconds.
• spf-wait—Maximum wait time in milliseconds for
SPF calculations. The range is from 1 to 600000 in
milliseconds.
Step 11
ospf log-adj-changes
(Optional) Sends syslog message when a neighbor state
changes.
Example:
Switch(config)# ospf log-adj-changes
Step 12
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 13
show ip ospf [process-id [area-id]] database
Displays lists of information related to the OSPF database
for a specific router.
Example:
Switch# show ip ospf database
Step 14
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Related Topics
Configuring OSPF Interfaces, on page 47
Monitoring OSPF, on page 57
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LSA Group Pacing
The OSPF LSA group pacing feature allows the router to group OSPF LSAs and pace the refreshing,
check-summing, and aging functions for more efficient router use. This feature is enabled by default with a
4-minute default pacing interval, and you will not usually need to modify this parameter. The optimum group
pacing interval is inversely proportional to the number of LSAs the router is refreshing, check-summing, and
aging. For example, if you have approximately 10,000 LSAs in the database, decreasing the pacing interval
would benefit you. If you have a very small database (40 to 100 LSAs), increasing the pacing interval to 10
to 20 minutes might benefit you slightly.
Changing LSA Group Pacing
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router ospf process-id
Enables OSPF routing, and enter router
configuration mode.
Example:
Switch(config)# router ospf 25
Step 3
timers lsa-group-pacing seconds
Changes the group pacing of LSAs.
Example:
Switch(config-router)# timers lsa-group-pacing 15
Step 4
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 5
show running-config
Verifies your entries.
Example:
Switch# show running-config
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration
file.
Example:
Switch# copy running-config startup-config
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How to Configure OSPF
Loopback Interfaces
OSPF uses the highest IP address configured on the interfaces as its router ID. If this interface is down or
removed, the OSPF process must recalculate a new router ID and resend all its routing information out its
interfaces. If a loopback interface is configured with an IP address, OSPF uses this IP address as its router
ID, even if other interfaces have higher IP addresses. Because loopback interfaces never fail, this provides
greater stability. OSPF automatically prefers a loopback interface over other interfaces, and it chooses the
highest IP address among all loopback interfaces.
Configuring a Loopback Interface
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
interface loopback 0
Creates a loopback interface, and enter interface
configuration mode.
Example:
Switch(config)# interface loopback 0
Step 3
ip address address mask
Assign an IP address to this interface.
Example:
Switch(config-if)# ip address 10.1.1.5
255.255.240.0
Step 4
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 5
show ip interface
Verifies your entries.
Example:
Switch# show ip interface
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Monitoring OSPF
Step 6
Command or Action
Purpose
copy running-config startup-config
(Optional) Saves your entries in the configuration
file.
Example:
Switch# copy running-config startup-config
Monitoring OSPF
You can display specific statistics such as the contents of IP routing tables, caches, and databases.
Table 6: Show IP OSPF Statistics Commands
show ip ospf [process-id]
Displays general information about
OSPF routing processes.
show ip ospf [process-id] database [router] [link-state-id]
Displays lists of information related to
the OSPF database.
show ip ospf [process-id] database [router] [self-originate]
show ip ospf [process-id] database [router] [adv-router
[ip-address]]
show ip ospf [process-id] database [network] [link-state-id]
show ip ospf [process-id] database [summary] [link-state-id]
show ip ospf [process-id] database [asbr-summary] [link-state-id]
show ip ospf [process-id] database [external] [link-state-id]
show ip ospf [process-id area-id] database [database-summary]
show ip ospf border-routes
Displays the internal OSPF routing
ABR and ASBR table entries.
show ip ospf interface [interface-name]
Displays OSPF-related interface
information.
show ip ospf neighbor [interface-name] [neighbor-id] detail
Displays OSPF interface neighbor
information.
show ip ospf virtual-links
Displays OSPF-related virtual links
information.
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Information About EIGRP
Related Topics
Configuring Other OSPF Parameters, on page 52
Information About EIGRP
Enhanced IGRP (EIGRP) is a Cisco proprietary enhanced version of the IGRP. EIGRP uses the same distance
vector algorithm and distance information as IGRP; however, the convergence properties and the operating
efficiency of EIGRP are significantly improved.
The convergence technology employs an algorithm referred to as the Diffusing Update Algorithm (DUAL),
which guarantees loop-free operation at every instant throughout a route computation and allows all devices
involved in a topology change to synchronize at the same time. Routers that are not affected by topology
changes are not involved in recomputations.
IP EIGRP provides increased network width. With RIP, the largest possible width of your network is 15 hops.
Because the EIGRP metric is large enough to support thousands of hops, the only barrier to expanding the
network is the transport-layer hop counter. EIGRP increments the transport control field only when an IP
packet has traversed 15 routers and the next hop to the destination was learned through EIGRP. When a RIP
route is used as the next hop to the destination, the transport control field is incremented as usual.
EIGRP Features
EIGRP offers these features:
• Fast convergence.
• Incremental updates when the state of a destination changes, instead of sending the entire contents of
the routing table, minimizing the bandwidth required for EIGRP packets.
• Less CPU usage because full update packets need not be processed each time they are received.
• Protocol-independent neighbor discovery mechanism to learn about neighboring routers.
• Variable-length subnet masks (VLSMs).
• Arbitrary route summarization.
• EIGRP scales to large networks.
EIGRP Components
EIGRP has these four basic components:
• Neighbor discovery and recovery is the process that routers use to dynamically learn of other routers on
their directly attached networks. Routers must also discover when their neighbors become unreachable
or inoperative. Neighbor discovery and recovery is achieved with low overhead by periodically sending
small hello packets. As long as hello packets are received, the Cisco IOS software can learn that a
neighbor is alive and functioning. When this status is determined, the neighboring routers can exchange
routing information.
• The reliable transport protocol is responsible for guaranteed, ordered delivery of EIGRP packets to all
neighbors. It supports intermixed transmission of multicast and unicast packets. Some EIGRP packets
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How to Configure EIGRP
must be sent reliably, and others need not be. For efficiency, reliability is provided only when necessary.
For example, on a multiaccess network that has multicast capabilities (such as Ethernet), it is not necessary
to send hellos reliably to all neighbors individually. Therefore, EIGRP sends a single multicast hello
with an indication in the packet informing the receivers that the packet need not be acknowledged. Other
types of packets (such as updates) require acknowledgment, which is shown in the packet. The reliable
transport has a provision to send multicast packets quickly when there are unacknowledged packets
pending. Doing so helps ensure that convergence time remains low in the presence of varying speed
links.
• The DUAL finite state machine embodies the decision process for all route computations. It tracks all
routes advertised by all neighbors. DUAL uses the distance information (known as a metric) to select
efficient, loop-free paths. DUAL selects routes to be inserted into a routing table based on feasible
successors. A successor is a neighboring router used for packet forwarding that has a least-cost path to
a destination that is guaranteed not to be part of a routing loop. When there are no feasible successors,
but there are neighbors advertising the destination, a recomputation must occur. This is the process
whereby a new successor is determined. The amount of time it takes to recompute the route affects the
convergence time. Recomputation is processor-intensive; it is advantageous to avoid recomputation if
it is not necessary. When a topology change occurs, DUAL tests for feasible successors. If there are
feasible successors, it uses any it finds to avoid unnecessary recomputation.
• The protocol-dependent modules are responsible for network layer protocol-specific tasks. An example
is the IP EIGRP module, which is responsible for sending and receiving EIGRP packets that are
encapsulated in IP. It is also responsible for parsing EIGRP packets and informing DUAL of the new
information received. EIGRP asks DUAL to make routing decisions, but the results are stored in the IP
routing table. EIGRP is also responsible for redistributing routes learned by other IP routing protocols.
Note
To enable EIGRP, the Switch or stack master must be running the IP services feature
set.
How to Configure EIGRP
To create an EIGRP routing process, you must enable EIGRP and associate networks. EIGRP sends updates
to the interfaces in the specified networks. If you do not specify an interface network, it is not advertised in
any EIGRP update.
Note
If you have routers on your network that are configured for IGRP, and you want to change to EIGRP, you
must designate transition routers that have both IGRP and EIGRP configured. In these cases, perform
Steps 1 through 3 in the next section and also see the “Configuring Split Horizon” section. You must use
the same AS number for routes to be automatically redistributed.
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Default EIGRP Configuration
Default EIGRP Configuration
Table 7: Default EIGRP Configuration
Feature
Default Setting
Auto summary
Disabled.
Subprefixes are summarized to the classful network boundary
when crossing classful network boundaries.
Default-information
Exterior routes are accepted and default information is passed
between EIGRP processes when doing redistribution.
Default metric
Only connected routes and interface static routes can be
redistributed without a default metric. The metric includes:
• Bandwidth: 0 or greater kb/s.
• Delay (tens of microseconds): 0 or any positive number that
is a multiple of 39.1 nanoseconds.
• Reliability: any number between 0 and 255 (255 means
100 percent reliability).
• Loading: effective bandwidth as a number between 0 and
255 (255 is 100 percent loading).
• MTU: maximum transmission unit size of the route in bytes.
0 or any positive integer.
Distance
Internal distance: 90.
External distance: 170.
EIGRP log-neighbor changes
Disabled. No adjacency changes logged.
IP authentication key-chain
No authentication provided.
IP authentication mode
No authentication provided.
IP bandwidth-percent
50 percent.
IP hello interval
For low-speed nonbroadcast multiaccess (NBMA) networks:
60 seconds; all other networks: 5 seconds.
IP hold-time
For low-speed NBMA networks: 180 seconds; all other networks:
15 seconds.
IP split-horizon
Enabled.
IP summary address
No summary aggregate addresses are predefined.
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Default EIGRP Configuration
Feature
Default Setting
Metric weights
tos: 0; k1 and k3: 1; k2, k4, and k5: 0
Network
None specified.
Nonstop Forwarding (NSF) Awareness Enabled for IPv4 on switches running the IP services feature set.
Allows Layer 3 switches to continue forwarding packets from a
neighboring NSF-capable router during hardware or software
changes.
NSF capability
Disabled.
Note
The Switch supports EIGRP NSF-capable routing for
IPv4.
Offset-list
Disabled.
Router EIGRP
Disabled.
Set metric
No metric set in the route map.
Traffic-share
Distributed proportionately to the ratios of the metrics.
Variance
1 (equal-cost load-balancing).
EIGRP Nonstop Forwarding
The Switch stack supports two levels of EIGRP nonstop forwarding:
• EIGRP NSF Awareness
• EIGRP NSF Capability
EIGRP NSF Awareness
The IP-services feature set supports EIGRP NSF Awareness for IPv4. When the neighboring router is
NSF-capable, the Layer 3 Switch continues to forward packets from the neighboring router during the interval
between the primary Route Processor (RP) in a router failing and the backup RP taking over, or while the
primary RP is manually reloaded for a nondisruptive software upgrade.
This feature cannot be disabled. For more information on this feature, see the “EIGRP Nonstop Forwarding
(NSF) Awareness” section of the Cisco IOS IP Routing Protocols Configuration Guide, Release 12.4.
EIGRP NSF Capability
The IP services feature set supports EIGRP Cisco NSF routing to speed up convergence and to eliminate
traffic loss after a stack master change. For details about this NSF capability, see the “Configuring Nonstop
Forwarding” chapter in the High Availability Configuration Guide, Cisco IOS XE Release 3S.
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The IP-services feature set also supports EIGRP NSF-capable routing for IPv4 for better convergence and
lower traffic loss following a stack master change. When an EIGRP NSF-capable stack master restarts or a
new stack master starts up and NSF restarts, the Switch has no neighbors, and the topology table is empty.
The Switch must bring up the interfaces, reacquire neighbors, and rebuild the topology and routing tables
without interrupting the traffic directed toward the Switch stack. EIGRP peer routers maintain the routes
learned from the new stack master and continue forwarding traffic through the NSF restart process.
To prevent an adjacency reset by the neighbors, the new stack master uses a new Restart (RS) bit in the EIGRP
packet header to show the restart. When the neighbor receives this, it synchronizes the stack in its peer list
and maintains the adjacency with the stack. The neighbor then sends its topology table to the stack master
with the RS bit set to show that it is NSF-aware and is aiding the new stack master.
If at least one of the stack peer neighbors is NSF-aware, the stack master receives updates and rebuilds its
database. Each NSF-aware neighbor sends an end of table (EOT) marker in the last update packet to mark the
end of the table content. The stack master recognizes the convergence when it receives the EOT marker, and
it then begins sending updates. When the stack master has received all EOT markers from its neighbors or
when the NSF converge timer expires, EIGRP notifies the routing information database (RIB) of convergence
and floods its topology table to all NSF-aware peers.
Note
NSF is not supported on interfaces configured for Hot Standby Router Protocol (HSRP).
Use the nsf EIGRP routing configuration command to enable EIGRP NSF routing. Use the show ip protocols
privileged EXEC command to verify that NSF is enabled on the device. See the command reference for this
release for information about the nsf command.
Configuring Basic EIGRP Parameters
Before You Begin
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router eigrp autonomous-system
Example:
Enables an EIGRP routing process, and enter router configuration
mode. The AS number identifies the routes to other EIGRP
routers and is used to tag routing information.
Switch(config)# router eigrp 10
Step 3
nsf
(Optional) Enables EIGRP NSF. Enter this command on the
stack master and on all of its peers.
Example:
Switch(config)# nsf
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Step 4
Command or Action
Purpose
network network-number
Associate networks with an EIGRP routing process. EIGRP sends
updates to the interfaces in the specified networks.
Example:
Switch(config)# network 192.168.0.0
Step 5
eigrp log-neighbor-changes
(Optional) Enables logging of EIGRP neighbor changes to
monitor routing system stability.
Example:
Switch(config)# eigrp log-neighbor-changes
Step 6
metric weights tos k1 k2 k3 k4 k5
Example:
(Optional) Adjust the EIGRP metric. Although the defaults have
been carefully set to provide excellent operation in most
networks, you can adjust them.
Switch(config)# metric weights 0 2 0 2 0 0 Caution
Step 7
offset-list [access-list number | name] {in | out}
offset [type number]
Setting metrics is complex and is not recommended
without guidance from an experienced network
designer.
(Optional) Applies an offset list to routing metrics to increase
incoming and outgoing metrics to routes learned through EIGRP.
You can limit the offset list with an access list or an interface.
Example:
Switch(config)# offset-list 21 out 10
Step 8
(Optional) Enables automatic summarization of subnet routes
into network-level routes.
auto-summary
Example:
Switch(config)# auto-summary
Step 9
ip summary-address eigrp
autonomous-system-number address mask
(Optional) Configures a summary aggregate.
Example:
Switch(config)# ip summary-address eigrp 1
192.168.0.0 255.255.0.0
Step 10
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 11
Verifies your entries.
show ip protocols
For NSF awareness, the output shows:
Example:
*** IP Routing is NSF aware *** EIGRP NSF enabled
Switch# show ip protocols
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Configuring EIGRP Interfaces
Step 12
Command or Action
Purpose
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Configuring EIGRP Interfaces
Other optional EIGRP parameters can be configured on an interface basis.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
interface interface-id
Enters interface configuration mode, and specifies the Layer 3
interface to configure.
Example:
Switch(config)# interface gigabitethernet
1/0/1
Step 3
ip bandwidth-percent eigrp percent
(Optional) Configures the percentage of bandwidth that can be
used by EIGRP on an interface. The default is 50 percent.
Example:
Switch(config-if)# ip bandwidth-percent eigrp
60
Step 4
ip summary-address eigrp
autonomous-system-number address mask
(Optional) Configures a summary aggregate address for a
specified interface (not usually necessary if auto-summary is
enabled).
Example:
Switch(config-if)# ip summary-address eigrp
109 192.161.0.0 255.255.0.0
Step 5
ip hello-interval eigrp autonomous-system-number (Optional) Change the hello time interval for an EIGRP routing
process. The range is 1 to 65535 seconds. The default is 60
seconds
seconds for low-speed NBMA networks and 5 seconds for all
other networks.
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Configuring EIGRP Route Authentication
Command or Action
Purpose
Example:
Switch(config-if)# ip hello-interval eigrp
109 10
Step 6
ip hold-time eigrp autonomous-system-number
seconds
Example:
(Optional) Change the hold time interval for an EIGRP routing
process. The range is 1 to 65535 seconds. The default is 180
seconds for low-speed NBMA networks and 15 seconds for all
other networks.
Switch(config-if)# ip hold-time eigrp 109 40 Caution
Step 7
Do not adjust the hold time without consulting Cisco
technical support.
no ip split-horizon eigrp autonomous-system-number (Optional) Disables split horizon to allow route information to
be advertised by a router out any interface from which that
information originated.
Example:
Switch(config-if)# no ip split-horizon eigrp
109
Step 8
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 9
Displays which interfaces EIGRP is active on and information
about EIGRP relating to those interfaces.
show ip eigrp interface
Example:
Switch# show ip eigrp interface
Step 10
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Configuring EIGRP Route Authentication
EIGRP route authentication provides MD5 authentication of routing updates from the EIGRP routing protocol
to prevent the introduction of unauthorized or false routing messages from unapproved sources.
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Configuring EIGRP Route Authentication
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
interface interface-id
Enters interface configuration mode, and specifies the Layer
3 interface to configure.
Example:
Switch(config)# interface gigabitethernet
1/0/1
Step 3
ip authentication mode eigrp autonomous-system
md5
Enables MD5 authentication in IP EIGRP packets.
Example:
Switch(config-if)# ip authentication mode
eigrp 104 md5
Step 4
ip authentication key-chain eigrp autonomous-system Enables authentication of IP EIGRP packets.
key-chain
Example:
Switch(config-if)# ip authentication key-chain
eigrp 105 chain1
Step 5
exit
Returns to global configuration mode.
Example:
Switch(config-if)# exit
Step 6
key chain name-of-chain
Identify a key chain and enter key-chain configuration mode.
Match the name configured in Step 4.
Example:
Switch(config)# key chain chain1
Step 7
key number
In key-chain configuration mode, identify the key number.
Example:
Switch(config-keychain)# key 1
Step 8
key-string text
In key-chain key configuration mode, identify the key string.
Example:
Switch(config-keychain-key)# key-string key1
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EIGRP Stub Routing
Step 9
Command or Action
Purpose
accept-lifetime start-time {infinite | end-time |
duration seconds}
(Optional) Specifies the time period during which the key
can be received.
Example:
Switch(config-keychain-key)# accept-lifetime
13:30:00 Jan 25 2011 duration 7200
Step 10
send-lifetime start-time {infinite | end-time | duration (Optional) Specifies the time period during which the key
can be sent.
seconds}
Example:
Switch(config-keychain-key)# send-lifetime
14:00:00 Jan 25 2011 duration 3600
Step 11
The start-time and end-time syntax can be either hh:mm:ss
Month date year or hh:mm:ss date Month year. The default
is forever with the default start-time and the earliest
acceptable date as January 1, 1993. The default end-time and
duration is infinite.
The start-time and end-time syntax can be either hh:mm:ss
Month date year or hh:mm:ss date Month year. The default
is forever with the default start-time and the earliest
acceptable date as January 1, 1993. The default end-time and
duration is infinite.
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 12
Displays authentication key information.
show key chain
Example:
Switch# show key chain
Step 13
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
EIGRP Stub Routing
The EIGRP stub routing feature reduces resource utilization by moving routed traffic closer to the end user.
Note
The feature set contains EIGRP stub routing capability, which only advertises connected or summary
routes from the routing tables to other Switches in the network. The Switch uses EIGRP stub routing at
the access layer to eliminate the need for other types of routing advertisements.
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Monitoring and Maintaining EIGRP
In a network using EIGRP stub routing, the only allowable route for IP traffic to the user is through a Switch
that is configured with EIGRP stub routing. The Switch sends the routed traffic to interfaces that are configured
as user interfaces or are connected to other devices.
When using EIGRP stub routing, you need to configure the distribution and remote routers to use EIGRP and
to configure only the Switch as a stub. Only specified routes are propagated from the Switch. The Switch
responds to all queries for summaries, connected routes, and routing updates.
Any neighbor that receives a packet informing it of the stub status does not query the stub router for any
routes, and a router that has a stub peer does not query that peer. The stub router depends on the distribution
router to send the proper updates to all peers.
In the figure given below, Switch B is configured as an EIGRP stub router. Switches A and C are connected
to the rest of the WAN. Switch B advertises connected, static, redistribution, and summary routes to Switch
A and C. Switch B does not advertise any routes learned from Switch A (and the reverse).
Figure 4: EIGRP Stub Router Configuration
For more information about EIGRP stub routing, see “Configuring EIGRP Stub Routing” section of the Cisco
IOS IP Configuration Guide, Volume 2 of 3: Routing Protocols.
Monitoring and Maintaining EIGRP
You can delete neighbors from the neighbor table. You can also display various EIGRP routing statistics. The
table given below lists the privileged EXEC commands for deleting neighbors and displaying statistics. For
explanations of fields in the resulting display, see the Cisco IOS IP Command Reference, Volume 2 of 3:
Routing Protocols, Release 12.4.
Table 8: IP EIGRP Clear and Show Commands
clear ip eigrp neighbors [if-address | interface]
Deletes neighbors from the neighbor table.
show ip eigrp interface [interface] [as number]
Displays information about interfaces configured for
EIGRP.
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Information About BGP
show ip eigrp neighbors [type-number]
Displays EIGRP discovered neighbors.
show ip eigrp topology
[autonomous-system-number] | [[ip-address] mask]]
Displays the EIGRP topology table for a given
process.
show ip eigrp traffic [autonomous-system-number]
Displays the number of packets sent and received
for all or a specified EIGRP process.
Information About BGP
The Border Gateway Protocol (BGP) is an exterior gateway protocol used to set up an interdomain routing
system that guarantees the loop-free exchange of routing information between autonomous systems.
Autonomous systems are made up of routers that operate under the same administration and that run Interior
Gateway Protocols (IGPs), such as RIP or OSPF, within their boundaries and that interconnect by using an
Exterior Gateway Protocol (EGP). BGP Version 4 is the standard EGP for interdomain routing in the Internet.
The protocol is defined in RFCs 1163, 1267, and 1771. You can find detailed information about BGP in
Internet Routing Architectures, published by Cisco Press, and in the “Configuring BGP” chapter in the Cisco
IP and IP Routing Configuration Guide.
For details about BGP commands and keywords, see the “IP Routing Protocols” part of the Cisco IOS IP
Command Reference, Volume 2 of 3: Routing Protocols .
BGP Network Topology
Routers that belong to the same autonomous system (AS) and that exchange BGP updates run internal BGP
(IBGP), and routers that belong to different autonomous systems and that exchange BGP updates run external
BGP (EBGP). Most configuration commands are the same for configuring EBGP and IBGP. The difference
is that the routing updates are exchanged either between autonomous systems (EBGP) or within an AS (IBGP).
The figure given below shows a network that is running both EBGP and IBGP.
Figure 5: EBGP, IBGP, and Multiple Autonomous Systems
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How to Configure BGP
Before exchanging information with an external AS, BGP ensures that networks within the AS can be reached
by defining internal BGP peering among routers within the AS and by redistributing BGP routing information
to IGPs that run within the AS, such as IGRP and OSPF.
Routers that run a BGP routing process are often referred to as BGP speakers. BGP uses the Transmission
Control Protocol (TCP) as its transport protocol (specifically port 179). Two BGP speakers that have a TCP
connection to each other for exchanging routing information are known as peers or neighbors. In the above
figure, Routers A and B are BGP peers, as are Routers B and C and Routers C and D. The routing information
is a series of AS numbers that describe the full path to the destination network. BGP uses this information to
construct a loop-free map of autonomous systems.
The network has these characteristics:
• Routers A and B are running EBGP, and Routers B and C are running IBGP. Note that the EBGP peers
are directly connected and that the IBGP peers are not. As long as there is an IGP running that allows
the two neighbors to reach one another, IBGP peers do not have to be directly connected.
• All BGP speakers within an AS must establish a peer relationship with each other. That is, the BGP
speakers within an AS must be fully meshed logically. BGP4 provides two techniques that reduce the
requirement for a logical full mesh: confederations and route reflectors.
• AS 200 is a transit AS for AS 100 and AS 300—that is, AS 200 is used to transfer packets between AS
100 and AS 300.
BGP peers initially exchange their full BGP routing tables and then send only incremental updates. BGP peers
also exchange keepalive messages (to ensure that the connection is up) and notification messages (in response
to errors or special conditions).
In BGP, each route consists of a network number, a list of autonomous systems that information has passed
through (the autonomous system path), and a list of other path attributes. The primary function of a BGP
system is to exchange network reachability information, including information about the list of AS paths,
with other BGP systems. This information can be used to determine AS connectivity, to prune routing loops,
and to enforce AS-level policy decisions.
A router or Switch running Cisco IOS does not select or use an IBGP route unless it has a route available to
the next-hop router and it has received synchronization from an IGP (unless IGP synchronization is disabled).
When multiple routes are available, BGP bases its path selection on attribute values. See the “Configuring
BGP Decision Attributes” section for information about BGP attributes.
BGP Version 4 supports classless interdomain routing (CIDR) so you can reduce the size of your routing
tables by creating aggregate routes, resulting in supernets. CIDR eliminates the concept of network classes
within BGP and supports the advertising of IP prefixes.
How to Configure BGP
Default BGP Configuration
The table given below shows the basic default BGP configuration. For the defaults for all characteristics, see
the specific commands in the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols,
Release 12.4.
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Default BGP Configuration
Table 9: Default BGP Configuration
Feature
Default Setting
Aggregate address
Disabled: None defined.
AS path access list
None defined.
Auto summary
Disabled.
Best path
• The router considers as-path in choosing a route and does not compare
similar routes from external BGP peers.
• Compare router ID: Disabled.
BGP community list
• Number: None defined. When you permit a value for the community
number, the list defaults to an implicit deny for everything else that
has not been permitted.
• Format: Cisco default format (32-bit number).
BGP confederation
identifier/peers
• Identifier: None configured.
• Peers: None identified.
BGP Fast external fallover
Enabled.
BGP local preference
100. The range is 0 to 4294967295 with the higher value preferred.
BGP network
None specified; no backdoor route advertised.
BGP route dampening
Disabled by default. When enabled:
• Half-life is 15 minutes.
• Re-use is 750 (10-second increments).
• Suppress is 2000 (10-second increments).
• Max-suppress-time is 4 times half-life; 60 minutes.
BGP router ID
The IP address of a loopback interface if one is configured or the highest
IP address configured for a physical interface on the router.
Default information originate
(protocol or network
redistribution)
Disabled.
Default metric
Built-in, automatic metric translations.
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Default BGP Configuration
Feature
Distance
Default Setting
• External route administrative distance: 20 (acceptable values are from
1 to 255).
• Internal route administrative distance: 200 (acceptable values are from
1 to 255).
• Local route administrative distance: 200 (acceptable values are from
1 to 255).
Distribute list
• In (filter networks received in updates): Disabled.
• Out (suppress networks from being advertised in updates): Disabled.
Internal route redistribution
Disabled.
IP prefix list
None defined.
Multi exit discriminator (MED)
• Always compare: Disabled. Does not compare MEDs for paths from
neighbors in different autonomous systems.
• Best path compare: Disabled.
• MED missing as worst path: Disabled.
• Deterministic MED comparison is disabled.
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Default BGP Configuration
Feature
Default Setting
Neighbor
• Advertisement interval: 30 seconds for external peers; 5 seconds for
internal peers.
• Change logging: Enabled.
• Conditional advertisement: Disabled.
• Default originate: No default route is sent to the neighbor.
• Description: None.
• Distribute list: None defined.
• External BGP multihop: Only directly connected neighbors are
allowed.
• Filter list: None used.
• Maximum number of prefixes received: No limit.
• Next hop (router as next hop for BGP neighbor): Disabled.
• Password: Disabled.
• Peer group: None defined; no members assigned.
• Prefix list: None specified.
• Remote AS (add entry to neighbor BGP table): No peers defined.
• Private AS number removal: Disabled.
• Route maps: None applied to a peer.
• Send community attributes: None sent to neighbors.
• Shutdown or soft reconfiguration: Not enabled.
• Timers: keepalive: 60 seconds; holdtime: 180 seconds.
• Update source: Best local address.
• Version: BGP Version 4.
• Weight: Routes learned through BGP peer: 0; routes sourced by the
local router: 32768.
NSF1 Awareness
Disabled2. If enabled, allows Layer 3 switches to continue forwarding
packets from a neighboring NSF-capable router during hardware or software
changes.
Route reflector
None configured.
Synchronization (BGP and
IGP)
Disabled.
Table map update
Disabled.
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Information About BGP Routing
Feature
Default Setting
Timers
Keepalive: 60 seconds; holdtime: 180 seconds.
1 Nonstop Forwarding
2 NSF Awareness can be enabled for IPv4 on switches with the IP services feature set by enabling Graceful Restart.
Nonstop Forwarding Awareness
The BGP NSF Awareness feature is supported for IPv4 in the IP services feature set. To enable this feature
with BGP routing, you need to enable Graceful Restart. When the neighboring router is NSF-capable, and
this feature is enabled, the Layer 3 Switch continues to forward packets from the neighboring router during
the interval between the primary Route Processor (RP) in a router failing and the backup RP taking over, or
while the primary RP is manually reloaded for a nondisruptive software upgrade.
For more information, see the “BGP Nonstop Forwarding (NSF) Awareness” section of the Cisco IOS IP
Routing Protocols Configuration Guide, Release 12.4.
Information About BGP Routing
To enable BGP routing, you establish a BGP routing process and define the local network. Because BGP must
completely recognize the relationships with its neighbors, you must also specify a BGP neighbor.
BGP supports two kinds of neighbors: internal and external. Internal neighbors are in the same AS; external
neighbors are in different autonomous systems. External neighbors are usually adjacent to each other and
share a subnet, but internal neighbors can be anywhere in the same AS.
The switch supports the use of private AS numbers, usually assigned by service providers and given to systems
whose routes are not advertised to external neighbors. The private AS numbers are from 64512 to 65535. You
can configure external neighbors to remove private AS numbers from the AS path by using the neighbor
remove-private-as router configuration command. Then when an update is passed to an external neighbor,
if the AS path includes private AS numbers, these numbers are dropped.
If your AS will be passing traffic through it from another AS to a third AS, it is important to be consistent
about the routes it advertises. If BGP advertised a route before all routers in the network had learned about
the route through the IGP, the AS might receive traffic that some routers could not yet route. To prevent this
from happening, BGP must wait until the IGP has propagated information across the AS so that BGP is
synchronized with the IGP. Synchronization is enabled by default. If your AS does not pass traffic from one
AS to another AS, or if all routers in your autonomous systems are running BGP, you can disable
synchronization, which allows your network to carry fewer routes in the IGP and allows BGP to converge
more quickly.
Enabling BGP Routing
Before You Begin
Note
To enable BGP, the switch or stack master must be running the IP services feature set.
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Enabling BGP Routing
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
Enables IP routing.
ip routing
Example:
Switch(config)# ip routing
Step 3
router bgp autonomous-system
Example:
Enables a BGP routing process, assign it an AS number, and enter
router configuration mode. The AS number can be from 1 to
65535, with 64512 to 65535 designated as private autonomous
numbers.
Switch(config)# router bgp 45000
Step 4
network network-number [mask network-mask] Configures a network as local to this AS, and enter it in the BGP
table.
[route-map route-map-name]
Example:
Switch(config)# network 10.108.0.0
Step 5
neighbor {ip-address | peer-group-name}
remote-as number
Adds an entry to the BGP neighbor table specifying that the
neighbor identified by the IP address belongs to the specified AS.
Example:
For EBGP, neighbors are usually directly connected, and the IP
address is the address of the interface at the other end of the
connection.
Switch(config)# neighbor 10.108.1.2
remote-as 65200
Step 6
neighbor {ip-address | peer-group-name}
remove-private-as
For IBGP, the IP address can be the address of any of the router
interfaces.
(Optional) Removes private AS numbers from the AS-path in
outbound routing updates.
Example:
Switch(config)# neighbor 172.16.2.33
remove-private-as
Step 7
(Optional) Enables synchronization between BGP and an IGP.
synchronization
Example:
Switch(config)# synchronization
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Enabling BGP Routing
Step 8
Command or Action
Purpose
auto-summary
(Optional) Enables automatic network summarization. When a
subnet is redistributed from an IGP into BGP, only the network
route is inserted into the BGP table.
Example:
Switch(config)# auto-summary
Step 9
bgp fast-external-fallover
Example:
(Optional) Automatically resets a BGP session when a link
between external neighbors goes down. By default, the session is
not immediately reset.
Switch(config)# bgp fast-external-fallover
Step 10
bgp graceful-restart
(Optional) Enables NSF awareness on switch. By default, NSF
awareness is disabled.
Example:
Switch(config)# bgp graceful-start
Step 11
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 12
show ip bgp network network-number
Verifies the configuration.
Example:
Switch# show ip bgp network 10.108.0.0
Step 13
show ip bgp neighbor
Verifies that NSF awareness (Graceful Restart) is enabled on the
neighbor.
Example:
If NSF awareness is enabled on the switch and the neighbor, this
message appears:
Switch# show ip bgp neighbor
Graceful Restart Capability: advertised and received
If NSF awareness is enabled on the switch, but not on the
neighbor, this message appears:
Graceful Restart Capability: advertised
Step 14
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
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Example: Configuring BGP on Routers
Example: Configuring BGP on Routers
These examples show how to configure BGP on the routers in the figure below,
Figure 6: EBGP, IBGP, and Multiple Autonomous Systems
Router A:
Switch(config)# router bgp 100
Switch(config-router)# neighbor 129.213.1.1 remote-as 200
Router B:
Switch(config)# router bgp 200
Switch(config-router)# neighbor 129.213.1.2 remote-as 100
Switch(config-router)# neighbor 175.220.1.2 remote-as 200
Router C:
Switch(config)# router bgp 200
Switch(config-router)# neighbor 175.220.212.1 remote-as 200
Switch(config-router)# neighbor 192.208.10.1 remote-as 300
Router D:
Switch(config)# router bgp 300
Switch(config-router)# neighbor 192.208.10.2 remote-as 200
To verify that BGP peers are running, use the show ip bgp neighbors privileged EXEC command. This is the
output of this command on Router A:
Switch# show ip bgp neighbors
BGP neighbor is 129.213.1.1, remote AS 200, external link
BGP version 4, remote router ID 175.220.212.1
BGP state = established, table version = 3, up for 0:10:59
Last read 0:00:29, hold time is 180, keepalive interval is 60 seconds
Minimum time between advertisement runs is 30 seconds
Received 2828 messages, 0 notifications, 0 in queue
Sent 2826 messages, 0 notifications, 0 in queue
Connections established 11; dropped 10
Anything other than state = established means that the peers are not running. The remote router ID is the
highest IP address on that router (or the highest loopback interface). Each time the table is updated with new
information, the table version number increments. A table version number that continually increments means
that a route is flapping, causing continual routing updates.
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Routing Policy Changes
For exterior protocols, a reference to an IP network from the network router configuration command controls
only which networks are advertised. This is in contrast to Interior Gateway Protocols (IGPs), such as EIGRP,
which also use the network command to specify where to send updates.
For detailed descriptions of BGP configuration, see the “IP Routing Protocols” part of the Cisco IOS IP
Configuration Guide, Release 12.4. For details about specific commands, see the Cisco IOS IP Command
Reference, Volume 2 of 3: Routing Protocols, Release 12.4.
Routing Policy Changes
Routing policies for a peer include all the configurations that might affect inbound or outbound routing table
updates. When you have defined two routers as BGP neighbors, they form a BGP connection and exchange
routing information. If you later change a BGP filter, weight, distance, version, or timer, or make a similar
configuration change, you must reset the BGP sessions so that the configuration changes take effect.
There are two types of reset, hard reset and soft reset. Cisco IOS Releases 12.1 and later support a soft reset
without any prior configuration. To use a soft reset without preconfiguration, both BGP peers must support
the soft route refresh capability, which is advertised in the OPEN message sent when the peers establish a
TCP session. A soft reset allows the dynamic exchange of route refresh requests and routing information
between BGP routers and the subsequent re-advertisement of the respective outbound routing table.
• When soft reset generates inbound updates from a neighbor, it is called dynamic inbound soft reset.
• When soft reset sends a set of updates to a neighbor, it is called outbound soft reset.
A soft inbound reset causes the new inbound policy to take effect. A soft outbound reset causes the new local
outbound policy to take effect without resetting the BGP session. As a new set of updates is sent during
outbound policy reset, a new inbound policy can also take effect.
The table given below lists the advantages and disadvantages hard reset and soft reset.
Table 10: Advantages and Disadvantages of Hard and Soft Resets
Type of Reset
Advantages
Disadvantages
Hard reset
No memory overhead
The prefixes in the BGP, IP, and FIB
tables provided by the neighbor are lost.
Not recommended.
Outbound soft reset
No configuration, no storing of routing
table updates
Does not reset inbound routing table
updates.
Dynamic inbound soft
reset
Does not clear the BGP session and cache Both BGP routers must support the route
Does not require storing of routing table refresh capability (in Cisco IOS Release
12.1 and later).
updates and has no memory overhead
Managing Routing Policy Changes
To learn if a BGP peer supports the route refresh capability and to reset the BGP session:
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BGP Decision Attributes
DETAILED STEPS
Step 1
Command or Action
Purpose
show ip bgp neighbors
Displays whether a neighbor supports the route refresh capability. When
supported, this message appears for the router:
Example:
Received route refresh capability from peer.
Switch# show ip bgp neighbors
Step 2
Step 3
clear ip bgp {* | address |
peer-group-name}
Resets the routing table on the specified connection.
• Enter an asterisk (*) to specify that all connections be reset.
Example:
• Enter an IP address to specify the connection to be reset.
Switch# clear ip bgp *
• Enter a peer group name to reset the peer group.
clear ip bgp {* | address |
peer-group-name} soft out
Example:
(Optional) Performs an outbound soft reset to reset the inbound routing
table on the specified connection. Use this command if route refresh is
supported.
• Enter an asterisk (*) to specify that all connections be reset.
Switch# clear ip bgp * soft out
• Enter an IP address to specify the connection to be reset.
• Enter a peer group name to reset the peer group.
Step 4
Verifies the reset by checking information about the routing table and
about BGP neighbors.
show ip bgp
Example:
Switch# show ip bgp
Step 5
Verifies the reset by checking information about the routing table and
about BGP neighbors.
show ip bgp neighbors
Example:
Switch# show ip bgp neighbors
BGP Decision Attributes
When a BGP speaker receives updates from multiple autonomous systems that describe different paths to the
same destination, it must choose the single best path for reaching that destination. When chosen, the selected
path is entered into the BGP routing table and propagated to its neighbors. The decision is based on the value
of attributes that the update contains and other BGP-configurable factors.
When a BGP peer learns two EBGP paths for a prefix from a neighboring AS, it chooses the best path and
inserts that path in the IP routing table. If BGP multipath support is enabled and the EBGP paths are learned
from the same neighboring autonomous systems, instead of a single best path, multiple paths are installed in
the IP routing table. Then, during packet switching, per-packet or per-destination load-balancing is performed
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BGP Decision Attributes
among the multiple paths. The maximum-paths router configuration command controls the number of paths
allowed.
These factors summarize the order in which BGP evaluates the attributes for choosing the best path:
1 If the path specifies a next hop that is inaccessible, drop the update. The BGP next-hop attribute,
automatically determined by the software, is the IP address of the next hop that is going to be used to reach
a destination. For EBGP, this is usually the IP address of the neighbor specified by the neighbor remote-as
router configuration command. You can disable next-hop processing by using route maps or the neighbor
next-hop-self router configuration command.
2 Prefer the path with the largest weight (a Cisco proprietary parameter). The weight attribute is local to the
router and not propagated in routing updates. By default, the weight attribute is 32768 for paths that the
router originates and zero for other paths. Routes with the largest weight are preferred. You can use access
lists, route maps, or the neighbor weight router configuration command to set weights.
3 Prefer the route with the highest local preference. Local preference is part of the routing update and
exchanged among routers in the same AS. The default value of the local preference attribute is 100. You
can set local preference by using the bgp default local-preference router configuration command or by
using a route map.
4 Prefer the route that was originated by BGP running on the local router.
5 Prefer the route with the shortest AS path.
6 Prefer the route with the lowest origin type. An interior route or IGP is lower than a route learned by EGP,
and an EGP-learned route is lower than one of unknown origin or learned in another way.
7 Prefer the route with the lowest multi -exit discriminator (MED) metric attribute if the neighboring AS is
the same for all routes considered. You can configure the MED by using route maps or by using the
default-metric router configuration command. When an update is sent to an IBGP peer, the MED is
included.
8 Prefer the external (EBGP) path over the internal (IBGP) path.
9 Prefer the route that can be reached through the closest IGP neighbor (the lowest IGP metric). This means
that the router will prefer the shortest internal path within the AS to reach the destination (the shortest path
to the BGP next-hop).
10 If the following conditions are all true, insert the route for this path into the IP routing table:
Both the best route and this route are external.
Both the best route and this route are from the same neighboring autonomous system.
Maximum-paths is enabled.
11 If multipath is not enabled, prefer the route with the lowest IP address value for the BGP router ID. The
router ID is usually the highest IP address on the router or the loopback (virtual) address, but might be
implementation-specific.
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Configuring IP Unicast Routing
Configuring BGP Decision Attributes
Configuring BGP Decision Attributes
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router bgp autonomous-system
Enables a BGP routing process, assign it an AS number, and enter
router configuration mode.
Example:
Switch(config)# router bgp 4500
Step 3
bgp best-path as-path ignore
(Optional) Configures the router to ignore AS path length in selecting
a route.
Example:
Switch(config-router)# bgp bestpath
as-path ignore
Step 4
neighbor {ip-address | peer-group-name}
next-hop-self
(Optional) Disables next-hop processing on BGP updates to a
neighbor by entering a specific IP address to be used instead of the
next-hop address.
Example:
Switch(config-router)# neighbor
10.108.1.1 next-hop-self
Step 5
neighbor {ip-address | peer-group-name} weight (Optional) Assign a weight to a neighbor connection. Acceptable
values are from 0 to 65535; the largest weight is the preferred route.
weight
Routes learned through another BGP peer have a default weight of
0; routes sourced by the local router have a default weight of 32768.
Example:
Switch(config-router)# neighbor
172.16.12.1 weight 50
Step 6
default-metric number
(Optional) Sets a MED metric to set preferred paths to external
neighbors. All routes without a MED will also be set to this value.
The range is 1 to 4294967295. The lowest value is the most
desirable.
Example:
Switch(config-router)# default-metric 300
Step 7
bgp bestpath med missing-as-worst
Example:
(Optional) Configures the switch to consider a missing MED as
having a value of infinity, making the path without a MED value
the least desirable path.
Switch(config-router)# bgp bestpath med
missing-as-worst
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Configuring BGP Decision Attributes
Step 8
Command or Action
Purpose
bgp always-compare med
(Optional) Configures the switch to compare MEDs for paths from
neighbors in different autonomous systems. By default, MED
comparison is only done among paths in the same AS.
Example:
Switch(config-router)# bgp
always-compare-med
Step 9
bgp bestpath med confed
Example:
(Optional) Configures the switch to consider the MED in choosing
a path from among those advertised by different subautonomous
systems within a confederation.
Switch(config-router)# bgp bestpath med
confed
Step 10
bgp deterministic med
Example:
(Optional) Configures the switch to consider the MED variable when
choosing among routes advertised by different peers in the same
AS.
Switch(config-router)# bgp deterministic
med
Step 11
bgp default local-preference value
Example:
(Optional) Change the default local preference value. The range is
0 to 4294967295; the default value is 100. The highest local
preference value is preferred.
Switch(config-router)# bgp default
local-preference 200
Step 12
maximum-paths number
Example:
Switch(config-router)# maximum-paths 8
Step 13
end
(Optional) Configures the number of paths to be added to the IP
routing table. The default is to only enter the best path in the routing
table. The range is from 1 to 16. Having multiple paths allows
load-balancing among the paths. (Although the switch software
allows a maximum of 32 equal-cost routes, the switch hardware will
never use more than 16 paths per route.)
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 14
show ip bgp
Verifies the reset by checking information about the routing table
and about BGP neighbors.
Example:
Switch# show ip bgp
Step 15
show ip bgp neighbors
Verifies the reset by checking information about the routing table
and about BGP neighbors.
Example:
Switch# show ip bgp neighbors
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Configuring IP Unicast Routing
Route Maps
Step 16
Command or Action
Purpose
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config
startup-config
Route Maps
Within BGP, route maps can be used to control and to modify routing information and to define the conditions
by which routes are redistributed between routing domains. See the “Using Route Maps to Redistribute Routing
Information” section for more information about route maps. Each route map has a name that identifies the
route map (map tag) and an optional sequence number.
Configuring BGP Filtering with Route Maps
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
route-map map-tag [permit | deny]
[sequence-number]
Creates a route map, and enter route-map configuration mode.
Example:
Switch(config)# route-map set-peer-address
permit 10
Step 3
set ip next-hop ip-address [...ip-address]
[peer-address]
Example:
Switch(config)# set ip next-hop 10.1.1.3
(Optional) Sets a route map to disable next-hop processing
• In an inbound route map, set the next hop of matching
routes to be the neighbor peering address, overriding
third-party next hops.
• In an outbound route map of a BGP peer, set the next hop
to the peering address of the local router, disabling the
next-hop calculation.
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Configuring IP Unicast Routing
BGP Filtering
Step 4
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 5
show route-map [map-name]
Displays all route maps configured or only the one specified
to verify configuration.
Example:
Switch# show route-map
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
BGP Filtering
You can filter BGP advertisements by using AS-path filters, such as the as-path access-list global configuration
command and the neighbor filter-list router configuration command. You can also use access lists with the
neighbor distribute-list router configuration command. Distribute-list filters are applied to network numbers.
See the “Controlling Advertising and Processing in Routing Updates” section for information about the
distribute-list command.
You can use route maps on a per-neighbor basis to filter updates and to modify various attributes. A route
map can be applied to either inbound or outbound updates. Only the routes that pass the route map are sent
or accepted in updates. On both inbound and outbound updates, matching is supported based on AS path,
community, and network numbers. Autonomous system path matching requires the match as-path access-list
route-map command, community based matching requires the match community-list route-map command,
and network-based matching requires the ip access-list global configuration command.
Configuring BGP Filtering by Neighbor
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
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Configuring IP Unicast Routing
Configuring BGP Filtering by Access Lists and Neighbors
Step 2
Command or Action
Purpose
router bgp autonomous-system
Enables a BGP routing process, assign it an AS number,
and enter router configuration mode.
Example:
Switch(config)# router bgp 109
Step 3
neighbor {ip-address | peer-group name} distribute-list (Optional) Filters BGP routing updates to or from
neighbors as specified in an access list.
{access-list-number | name} {in | out}
Note
Example:
Switch(config-router)# neighbor 172.16.4.1
distribute-list 39 in
Step 4
neighbor {ip-address | peer-group name} route-map
map-tag {in | out}
You can also use the neighbor prefix-list router
configuration command to filter updates, but you
cannot use both commands to configure the same
BGP peer.
(Optional) Applies a route map to filter an incoming or
outgoing route.
Example:
Switch(config-router)# neighbor 172.16.70.24
route-map internal-map in
Step 5
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 6
show ip bgp neighbors
Verifies the configuration.
Example:
Switch# show ip bgp neighbors
Step 7
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Configuring BGP Filtering by Access Lists and Neighbors
Another method of filtering is to specify an access list filter on both incoming and outbound updates, based
on the BGP autonomous system paths. Each filter is an access list based on regular expressions. (See the
“Regular Expressions” appendix in the Cisco IOS Dial Technologies Command Reference, Release 12.4 for
more information on forming regular expressions.) To use this method, define an autonomous system path
access list, and apply it to updates to and from particular neighbors.
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Configuring IP Unicast Routing
Configuring BGP Filtering by Access Lists and Neighbors
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
ip as-path access-list access-list-number {permit | deny}
as-regular-expressions
Defines a BGP-related access list.
Example:
Switch(config)# ip as-path access-list 1 deny _65535_
Step 3
router bgp autonomous-system
Enters BGP router configuration mode.
Example:
Switch(config)# router bgp 110
Step 4
neighbor {ip-address | peer-group name} filter-list
{access-list-number | name} {in | out | weight weight}
Establishes a BGP filter based on an access
list.
Example:
Switch(config-router)# neighbor 172.16.1.1 filter-list
1 out
Step 5
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 6
show ip bgp neighbors [paths regular-expression]
Verifies the configuration.
Example:
Switch# show ip bgp neighbors
Step 7
copy running-config startup-config
(Optional) Saves your entries in the
configuration file.
Example:
Switch# copy running-config startup-config
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Configuring IP Unicast Routing
Prefix List for BGP Filtering
Prefix List for BGP Filtering
You can use prefix lists as an alternative to access lists in many BGP route filtering commands, including the
neighbor distribute-list router configuration command. The advantages of using prefix lists include
performance improvements in loading and lookup of large lists, incremental update support, easier CLI
configuration, and greater flexibility.
Filtering by a prefix list involves matching the prefixes of routes with those listed in the prefix list, as when
matching access lists. When there is a match, the route is used. Whether a prefix is permitted or denied is
based upon these rules:
• An empty prefix list permits all prefixes.
• An implicit deny is assumed if a given prefix does not match any entries in a prefix list.
• When multiple entries of a prefix list match a given prefix, the sequence number of a prefix list entry
identifies the entry with the lowest sequence number.
By default, sequence numbers are generated automatically and incremented in units of five. If you disable the
automatic generation of sequence numbers, you must specify the sequence number for each entry. You can
specify sequence values in any increment. If you specify increments of one, you cannot insert additional
entries into the list; if you choose very large increments, you might run out of values.
Configuring Prefix Lists for BGP Filtering
You do not need to specify a sequence number when removing a configuration entry. Show commands include
the sequence numbers in their output.
Before using a prefix list in a command, you must set up the prefix list.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
ip prefix-list list-name [seq seq-value] deny | permit
network/len [ge ge-value] [le le-value]
Example:
Switch(config)# ip prefix-list BLUE permit
172.16.1.0/24
Creates a prefix list with an optional sequence number to
deny or permit access for matching conditions. You must
enter at least one permit or deny clause.
• network/len is the network number and length (in bits)
of the network mask.
• (Optional) ge and le values specify the range of the
prefix length to be matched.The specified ge-value and
le-value must satisfy this condition: len < ge-value <
le-value < 32
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Configuring IP Unicast Routing
BGP Community Filtering
Step 3
Command or Action
Purpose
ip prefix-list list-name seq seq-value deny | permit
network/len [ge ge-value] [le le-value]
(Optional) Adds an entry to a prefix list, and assign a sequence
number to the entry.
Example:
Switch(config)# ip prefix-list BLUE seq 10
permit 172.24.1.0/24
Step 4
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 5
show ip prefix list [detail | summary] name
[network/len] [seq seq-num] [longer] [first-match]
Verifies the configuration by displaying information about a
prefix list or prefix list entries.
Example:
Switch# show ip prefix list summary test
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
BGP Community Filtering
One way that BGP controls the distribution of routing information based on the value of the COMMUNITIES
attribute. The attribute is a way to groups destinations into communities and to apply routing decisions based
on the communities. This method simplifies configuration of a BGP speaker to control distribution of routing
information.
A community is a group of destinations that share some common attribute. Each destination can belong to
multiple communities. AS administrators can define to which communities a destination belongs. By default,
all destinations belong to the general Internet community. The community is identified by the COMMUNITIES
attribute, an optional, transitive, global attribute in the numerical range from 1 to 4294967200. These are some
predefined, well-known communities:
• internet—Advertise this route to the Internet community. All routers belong to it.
• no-export—Do not advertise this route to EBGP peers.
• no-advertise—Do not advertise this route to any peer (internal or external).
• local-as—Do not advertise this route to peers outside the local autonomous system.
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Configuring IP Unicast Routing
Configuring BGP Community Filtering
Based on the community, you can control which routing information to accept, prefer, or distribute to other
neighbors. A BGP speaker can set, append, or modify the community of a route when learning, advertising,
or redistributing routes. When routes are aggregated, the resulting aggregate has a COMMUNITIES attribute
that contains all communities from all the initial routes.
You can use community lists to create groups of communities to use in a match clause of a route map. As
with an access list, a series of community lists can be created. Statements are checked until a match is found.
As soon as one statement is satisfied, the test is concluded.
To set the COMMUNITIES attribute and match clauses based on communities, see the match community-list
and set community route-map configuration commands in the “Using Route Maps to Redistribute Routing
Information” section.
Configuring BGP Community Filtering
By default, no COMMUNITIES attribute is sent to a neighbor. You can specify that the COMMUNITIES
attribute be sent to the neighbor at an IP address by using the neighbor send-community router configuration
command.
SUMMARY STEPS
1. configure terminal
2. ip community-list community-list-number {permit | deny} community-number
3. router bgp autonomous-system
4. neighbor {ip-address | peer-group name} send-community
5. set comm-list list-num delete
6. exit
7. ip bgp-community new-format
8. end
9. show ip bgp community
10. copy running-config startup-config
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
ip community-list community-list-number {permit Creates a community list, and assigns it a number.
| deny} community-number
• The community-list-number is an integer from 1 to 99 that
identifies one or more permit or deny groups of
Example:
communities.
Switch(config)# ip community-list 1 permit
50000:10
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Configuring IP Unicast Routing
Configuring BGP Community Filtering
Command or Action
Purpose
• The community-number is the number configured by a set
community route-map configuration command.
Step 3
router bgp autonomous-system
Enters BGP router configuration mode.
Example:
Switch(config)# router bgp 108
Step 4
neighbor {ip-address | peer-group name}
send-community
Specifies that the COMMUNITIES attribute be sent to the
neighbor at this IP address.
Example:
Switch(config-router)# neighbor 172.16.70.23
send-community
Step 5
set comm-list list-num delete
Example:
(Optional) Removes communities from the community attribute
of an inbound or outbound update that match a standard or
extended community list specified by a route map.
Switch(config-router)# set comm-list 500
delete
Step 6
exit
Returns to global configuration mode.
Example:
Switch(config-router)# end
Step 7
ip bgp-community new-format
(Optional) Displays and parses BGP communities in the format
AA:NN.
Example:
A BGP community is displayed in a two-part format 2 bytes
long. The Cisco default community format is in the format
NNAA. In the most recent RFC for BGP, a community takes
the form AA:NN, where the first part is the AS number and the
second part is a 2-byte number.
Switch(config)# ip bgp-community new format
Step 8
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 9
show ip bgp community
Verifies the configuration.
Example:
Switch# show ip bgp community
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Configuring IP Unicast Routing
BGP Neighbors and Peer Groups
Step 10
Command or Action
Purpose
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
BGP Neighbors and Peer Groups
Often many BGP neighbors are configured with the same update policies (that is, the same outbound route
maps, distribute lists, filter lists, update source, and so on). Neighbors with the same update policies can be
grouped into peer groups to simplify configuration and to make updating more efficient. When you have
configured many peers, we recommend this approach.
To configure a BGP peer group, you create the peer group, assign options to the peer group, and add neighbors
as peer group members. You configure the peer group by using the neighbor router configuration commands.
By default, peer group members inherit all the configuration options of the peer group, including the remote-as
(if configured), version, update-source, out-route-map, out-filter-list, out-dist-list,
minimum-advertisement-interval, and next-hop-self. All peer group members also inherit changes made to
the peer group. Members can also be configured to override the options that do not affect outbound updates.
Configuring BGP Neighbors and Peer Groups
To assign configuration options to an individual neighbor, specify any of these router configuration commands
by using the neighbor IP address. To assign the options to a peer group, specify any of the commands by using
the peer group name. You can disable a BGP peer or peer group without removing all the configuration
information by using the neighbor shutdown router configuration command.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router bgp autonomous-system
Enters BGP router configuration mode.
Step 3
neighbor peer-group-name peer-group
Creates a BGP peer group.
Step 4
neighbor ip-address peer-group peer-group-name Makes a BGP neighbor a member of the peer group.
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Configuring BGP Neighbors and Peer Groups
Command or Action
Purpose
Step 5
neighbor {ip-address | peer-group-name}
remote-as number
Specifies a BGP neighbor. If a peer group is not configured with
a remote-as number, use this command to create peer groups
containing EBGP neighbors. The range is 1 to 65535.
Step 6
neighbor {ip-address | peer-group-name}
description text
(Optional) Associates a description with a neighbor.
Step 7
neighbor {ip-address | peer-group-name}
default-originate [route-map map-name]
(Optional) Allows a BGP speaker (the local router) to send the
default route 0.0.0.0 to a neighbor for use as a default route.
Step 8
neighbor {ip-address | peer-group-name}
send-community
(Optional) Specifies that the COMMUNITIES attribute be sent
to the neighbor at this IP address.
Step 9
neighbor {ip-address | peer-group-name}
update-source interface
(Optional) Allows internal BGP sessions to use any operational
interface for TCP connections.
Step 10
neighbor {ip-address | peer-group-name}
ebgp-multihop
(Optional) Allows BGP sessions, even when the neighbor is not
on a directly connected segment. The multihop session is not
established if the only route to the multihop peer’s address is the
default route (0.0.0.0).
Step 11
neighbor {ip-address | peer-group-name} local-as (Optional) Specifies an AS number to use as the local AS. The
range is 1 to 65535.
number
Step 12
neighbor {ip-address | peer-group-name}
advertisement-interval seconds
(Optional) Sets the minimum interval between sending BGP
routing updates.
Step 13
neighbor {ip-address | peer-group-name}
maximum-prefix maximum [threshold]
(Optional) Controls how many prefixes can be received from a
neighbor. The range is 1 to 4294967295. The threshold (optional)
is the percentage of maximum at which a warning message is
generated. The default is 75 percent.
Step 14
neighbor {ip-address | peer-group-name}
next-hop-self
(Optional) Disables next-hop processing on the BGP updates to
a neighbor.
Step 15
neighbor {ip-address | peer-group-name} password (Optional) Sets MD5 authentication on a TCP connection to a
BGP peer. The same password must be configured on both BGP
string
peers, or the connection between them is not made.
Step 16
neighbor {ip-address | peer-group-name}
route-map map-name {in | out}
(Optional) Applies a route map to incoming or outgoing routes.
Step 17
neighbor {ip-address | peer-group-name}
send-community
(Optional) Specifies that the COMMUNITIES attribute be sent
to the neighbor at this IP address.
Step 18
neighbor {ip-address | peer-group-name} timers (Optional) Sets timers for the neighbor or peer group.
keepalive holdtime
• The keepalive interval is the time within which keepalive
messages are sent to peers. The range is 1 to 4294967295
seconds; the default is 60.
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Configuring IP Unicast Routing
Aggregate Routes
Command or Action
Purpose
• The holdtime is the interval after which a peer is declared
inactive after not receiving a keepalive message from it.
The range is 1 to 4294967295 seconds; the default is 180.
Step 19
neighbor {ip-address | peer-group-name} weight (Optional) Specifies a weight for all routes from a neighbor.
weight
Step 20
(Optional) Filter BGP routing updates to or from neighbors, as
neighbor {ip-address | peer-group-name}
distribute-list {access-list-number | name} {in | specified in an access list.
out}
Step 21
neighbor {ip-address | peer-group-name}
filter-list access-list-number {in | out | weight
weight}
Step 22
neighbor {ip-address | peer-group-name} version (Optional) Specifies the BGP version to use when
communicating with a neighbor.
value
Step 23
neighbor {ip-address | peer-group-name}
soft-reconfiguration inbound
(Optional) Configures the software to start storing received
updates.
Step 24
end
Returns to privileged EXEC mode.
(Optional) Establish a BGP filter.
Example:
Switch(config)# end
Step 25
show ip bgp neighbors
Verifies the configuration.
Step 26
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Aggregate Routes
Classless interdomain routing (CIDR) enables you to create aggregate routes (or supernets) to minimize the
size of routing tables. You can configure aggregate routes in BGP either by redistributing an aggregate route
into BGP or by creating an aggregate entry in the BGP routing table. An aggregate address is added to the
BGP table when there is at least one more specific entry in the BGP table.
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Configuring IP Unicast Routing
Configuring Aggregate Addresses in a Routing Table
Configuring Aggregate Addresses in a Routing Table
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router bgp autonomous-system
Enters BGP router configuration mode.
Example:
Switch(config)# router bgp 106
Step 3
aggregate-address address mask
Example:
Creates an aggregate entry in the BGP routing table. The
aggregate route is advertised as coming from the AS, and
the atomic aggregate attribute is set to indicate that
information might be missing.
Switch(config-router)# aggregate-address 10.0.0.0
255.0.0.0
Step 4
aggregate-address address mask as-set
Example:
Switch(config-router)# aggregate-address 10.0.0.0
255.0.0.0 as-set
Step 5
aggregate-address address-mask summary-only
(Optional) Generates AS set path information. This
command creates an aggregate entry following the same
rules as the previous command, but the advertised path
will be an AS_SET consisting of all elements contained
in all paths. Do not use this keyword when aggregating
many paths because this route must be continually
withdrawn and updated.
(Optional) Advertises summary addresses only.
Example:
Switch(config-router)# aggregate-address 10.0.0.0
255.0.0.0 summary-only
Step 6
aggregate-address address mask suppress-map
map-name
(Optional) Suppresses selected, more specific routes.
Example:
Switch(config-router)# aggregate-address 10.0.0.0
255.0.0.0 suppress-map map1
Step 7
aggregate-address address mask advertise-map
map-name
(Optional) Generates an aggregate based on conditions
specified by the route map.
Example:
Switch(config-router)# aggregate-address 10.0.0.0
255.0.0.0 advertise-map map2
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Configuring IP Unicast Routing
Routing Domain Confederations
Step 8
Command or Action
Purpose
aggregate-address address mask attribute-map
map-name
(Optional) Generates an aggregate with attributes specified
in the route map.
Example:
Switch(config-router)# aggregate-address 10.0.0.0
255.0.0.0 attribute-map map3
Step 9
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 10
show ip bgp neighbors [advertised-routes]
Verifies the configuration.
Example:
Switch# show ip bgp neighbors
Step 11
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Routing Domain Confederations
One way to reduce the IBGP mesh is to divide an autonomous system into multiple subautonomous systems
and to group them into a single confederation that appears as a single autonomous system. Each autonomous
system is fully meshed within itself and has a few connections to other autonomous systems in the same
confederation. Even though the peers in different autonomous systems have EBGP sessions, they exchange
routing information as if they were IBGP peers. Specifically, the next hop, MED, and local preference
information is preserved. You can then use a single IGP for all of the autonomous systems.
Configuring Routing Domain Confederations
You must specify a confederation identifier that acts as the autonomous system number for the group of
autonomous systems.
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Configuring Routing Domain Confederations
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router bgp autonomous-system
Enters BGP router configuration mode.
Example:
Switch(config)# router bgp 100
Step 3
bgp confederation identifier autonomous-system
Configures a BGP confederation identifier.
Example:
Switch(config)# bgp confederation identifier 50007
Step 4
bgp confederation peers autonomous-system
[autonomous-system ...]
Specifies the autonomous systems that belong to
the confederation and that will be treated as special
EBGP peers.
Example:
Switch(config)# bgp confederation peers 51000 51001
51002
Step 5
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 6
show ip bgp neighbor
Verifies the configuration.
Example:
Switch# show ip bgp neighbor
Step 7
show ip bgp network
Verifies the configuration.
Example:
Switch# show ip bgp network
Step 8
copy running-config startup-config
(Optional) Saves your entries in the configuration
file.
Example:
Switch# copy running-config startup-config
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BGP Route Reflectors
BGP Route Reflectors
BGP requires that all of the IBGP speakers be fully meshed. When a router receives a route from an external
neighbor, it must advertise it to all internal neighbors. To prevent a routing information loop, all IBPG speakers
must be connected. The internal neighbors do not send routes learned from internal neighbors to other internal
neighbors.
With route reflectors, all IBGP speakers need not be fully meshed because another method is used to pass
learned routes to neighbors. When you configure an internal BGP peer to be a route reflector, it is responsible
for passing IBGP learned routes to a set of IBGP neighbors. The internal peers of the route reflector are divided
into two groups: client peers and nonclient peers (all the other routers in the autonomous system). A route
reflector reflects routes between these two groups. The route reflector and its client peers form a cluster. The
nonclient peers must be fully meshed with each other, but the client peers need not be fully meshed. The
clients in the cluster do not communicate with IBGP speakers outside their cluster.
When the route reflector receives an advertised route, it takes one of these actions, depending on the neighbor:
• A route from an external BGP speaker is advertised to all clients and nonclient peers.
• A route from a nonclient peer is advertised to all clients.
• A route from a client is advertised to all clients and nonclient peers. Hence, the clients need not be fully
meshed.
Usually a cluster of clients have a single route reflector, and the cluster is identified by the route reflector
router ID. To increase redundancy and to avoid a single point of failure, a cluster might have more than one
route reflector. In this case, all route reflectors in the cluster must be configured with the same 4-byte cluster
ID so that a route reflector can recognize updates from route reflectors in the same cluster. All the route
reflectors serving a cluster should be fully meshed and should have identical sets of client and nonclient peers.
Configuring BGP Route Reflectors
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router bgp autonomous-system
Enters BGP router configuration mode.
Example:
Switch(config)# router bgp 101
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Route Dampening
Step 3
Command or Action
Purpose
neighbor {ip-address | peer-group-name}
route-reflector-client
Configures the local router as a BGP route reflector and the
specified neighbor as a client.
Example:
Switch(config-router)# neighbor 172.16.70.24
route-reflector-client
Step 4
bgp cluster-id cluster-id
(Optional) Configures the cluster ID if the cluster has more
than one route reflector.
Example:
Switch(config-router)# bgp cluster-id 10.0.1.2
Step 5
no bgp client-to-client reflection
Example:
(Optional) Disables client-to-client route reflection. By
default, the routes from a route reflector client are reflected
to other clients. However, if the clients are fully meshed,
the route reflector does not need to reflect routes to clients.
Switch(config-router)# no bgp client-to-client
reflection
Step 6
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 7
show ip bgp
Verifies the configuration. Displays the originator ID and
the cluster-list attributes.
Example:
Switch# show ip bgp
Step 8
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Route Dampening
Route flap dampening is a BGP feature designed to minimize the propagation of flapping routes across an
internetwork. A route is considered to be flapping when it is repeatedly available, then unavailable, then
available, then unavailable, and so on. When route dampening is enabled, a numeric penalty value is assigned
to a route when it flaps. When a route’s accumulated penalties reach a configurable limit, BGP suppresses
advertisements of the route, even if the route is running. The reuse limit is a configurable value that is compared
with the penalty. If the penalty is less than the reuse limit, a suppressed route that is up is advertised again.
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Configuring Route Dampening
Dampening is not applied to routes that are learned by IBGP. This policy prevents the IBGP peers from having
a higher penalty for routes external to the AS.
Configuring Route Dampening
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
router bgp autonomous-system
Enters BGP router configuration mode.
Example:
Switch(config)# router bgp 100
Step 3
Enables BGP route dampening.
bgp dampening
Example:
Switch(config-router)# bgp dampening
Step 4
bgp dampening half-life reuse suppress max-suppress
[route-map map]
(Optional) Changes the default values of route
dampening factors.
Example:
Switch(config-router)# bgp dampening 30 1500 10000
120
Step 5
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 6
show ip bgp flap-statistics [{regexp regexp} | {filter-list (Optional) Monitors the flaps of all paths that are
flapping. The statistics are deleted when the route is
list} | {address mask [longer-prefix]}]
not suppressed and is stable.
Example:
Switch# show ip bgp flap-statistics
Step 7
show ip bgp dampened-paths
(Optional) Displays the dampened routes, including
the time remaining before they are suppressed.
Example:
Switch# show pi bgp dampened-paths
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More BGP Information
Command or Action
Step 8
Purpose
clear ip bgp flap-statistics [{regexp regexp} | {filter-list (Optional) Clears BGP flap statistics to make it less
likely that a route will be dampened.
list} | {address mask [longer-prefix]}
Example:
Switch# clear ip bgp flap-statistics
Step 9
clear ip bgp dampening
(Optional) Clears route dampening information, and
unsuppress the suppressed routes.
Example:
Switch# clear ip bgp dampening
Step 10
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
More BGP Information
For detailed descriptions of BGP configuration, see the “Configuring BGP” chapter in the “IP Routing Protocols”
part of the Cisco IOS IP Configuration Guide, Release 12.4. For details about specific commands, see the
Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols, Release 12.4.
Monitoring and Maintaining BGP
You can remove all contents of a particular cache, table, or database. This might be necessary when the
contents of the particular structure have become or are suspected to be invalid.
You can display specific statistics, such as the contents of BGP routing tables, caches, and databases. You
can use the information to get resource utilization and solve network problems. You can also display information
about node reachability and discover the routing path your device’s packets are taking through the network.
The table given below lists the privileged EXEC commands for clearing and displaying BGP. For explanations
of the display fields, see the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols, Release 12.4.
Table 11: IP BGP Clear and Show Commands
clear ip bgp address
Resets a particular BGP connection.
clear ip bgp *
Resets all BGP connections.
clear ip bgp peer-group tag
Removes all members of a BGP peer group.
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show ip bgp prefix
Displays peer groups and peers not in peer groups to
which the prefix has been advertised. Also displays prefix
attributes such as the next hop and the local prefix.
show ip bgp cidr-only
Displays all BGP routes that contain subnet and supernet
network masks.
show ip bgp community [community-number]
[exact]
Displays routes that belong to the specified communities.
show ip bgp community-list
community-list-number [exact-match]
Displays routes that are permitted by the community list.
show ip bgp filter-list access-list-number
Displays routes that are matched by the specified AS path
access list.
show ip bgp inconsistent-as
Displays the routes with inconsistent originating
autonomous systems.
show ip bgp regexp regular-expression
Displays the routes that have an AS path that matches the
specified regular expression entered on the command line.
show ip bgp
Displays the contents of the BGP routing table.
show ip bgp neighbors [address]
Displays detailed information on the BGP and TCP
connections to individual neighbors.
show ip bgp neighbors [address]
[advertised-routes | dampened-routes |
flap-statistics | paths regular-expression |
received-routes | routes]
Displays routes learned from a particular BGP neighbor.
show ip bgp paths
Displays all BGP paths in the database.
show ip bgp peer-group [tag] [summary]
Displays information about BGP peer groups.
show ip bgp summary
Displays the status of all BGP connections.
The bgp log-neighbor changes command is enabled by default. It allows to log messages that are generated
when a BGP neighbor resets, comes up, or goes down.
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Information About ISO CLNS Routing
Information About ISO CLNS Routing
Connectionless Routing
The International Organization for Standardization (ISO) Connectionless Network Service (CLNS) protocol
is a standard for the network layer of the Open System Interconnection (OSI) model. Addresses in the ISO
network architecture are referred to as network service access point (NSAP) addresses and network entity
titles (NETs). Each node in an OSI network has one or more NETs. In addition, each node has many NSAP
addresses.
When you enable connectionless routing on the Switch by using the clns routing global configuration command,
the Switch makes only forwarding decisions, with no routing-related functionality. For dynamic routing, you
must also enable a routing protocol. The Switch supports the Intermediate System-to-Intermediate System
(IS-IS) dynamic routing protocol that is based on the OSI routing protocol for ISO CLNS networks.
When dynamically routing, you use IS-IS. This routing protocol supports the concept of areas. Within an area,
all routers know how to reach all the system IDs. Between areas, routers know how to reach the proper area.
IS-IS supports two levels of routing: station routing (within an area) and area routing (between areas).
The key difference between the ISO IGRP and IS-IS NSAP addressing schemes is in the definition of area
addresses. Both use the system ID for Level 1 routing (routing within an area). However, they differ in the
way addresses are specified for area routing. An ISO IGRP NSAP address includes three separate fields for
routing: the domain, area, and system ID. An IS-IS address includes two fields: a single continuous area field
(comprising the domain and area fields) and the system ID.
Note
For more detailed information about ISO CLNS, see the Cisco IOS Apollo Domain, Banyan VINES,
DECnet, ISO CLNS and XNS Configuration Guide, Release 12.4. For complete syntax and usage information
for the commands used in this chapter, see the Cisco IOS Apollo Domain, Banyan VINES, DECnet, ISO
CLNS and XNS Command Reference, Release 12.4, use the IOS command reference master index, or
search online.
How to Configure ISO CLNS Routing
IS-IS Dynamic Routing
IS-IS is an ISO dynamic routing protocol (described in ISO 105890). Unlike other routing protocols, enabling
IS-IS requires that you create an IS-IS routing process and assign it to a specific interface, rather than to a
network. You can specify more than one IS-IS routing process per Layer 3 Switch or router by using the
multiarea IS-IS configuration syntax. You then configure the parameters for each instance of the IS-IS routing
process.
Small IS-IS networks are built as a single area that includes all the routers in the network. As the network
grows larger, it is usually reorganized into a backbone area made up of the connected set of all Level 2 routers
from all areas, which is in turn connected to local areas. Within a local area, routers know how to reach all
system IDs. Between areas, routers know how to reach the backbone, and the backbone routers know how to
reach other areas.
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Default IS-IS Configuration
Routers establish Level 1 adjacencies to perform routing within a local area (station routing). Routers establish
Level 2 adjacencies to perform routing between Level 1 areas (area routing).
A single Cisco router can participate in routing in up to 29 areas and can perform Level 2 routing in the
backbone. In general, each routing process corresponds to an area. By default, the first instance of the routing
process configured performs both Level 1and Level 2 routing. You can configure additional router instances,
which are automatically treated as Level 1 areas. You must configure the parameters for each instance of the
IS-IS routing process individually.
For IS-IS multiarea routing, you can configure only one process to perform Level 2 routing, although you can
define up to 29 Level 1 areas for each Cisco unit. If Level 2 routing is configured on any process, all additional
processes are automatically configured as Level 1. You can configure this process to perform Level 1 routing
at the same time. If Level 2 routing is not desired for a router instance, remove the Level 2 capability using
the is-type global configuration command. Use the is-type command also to configure a different router
instance as a Level 2 router.
Note
For more detailed information about IS-IS, see the “IP Routing Protocols” chapter of the Cisco IOS IP
Configuration Guide, Release 12.4. For complete syntax and usage information for the commands used
in this section, see the Cisco IOS IP Command Reference, Release 12.4.
Default IS-IS Configuration
Table 12: Default IS-IS Configuration
Feature
Default Setting
Ignore link-state PDU (LSP) errors
Enabled.
IS-IS type
Conventional IS-IS: the router acts as both a Level 1 (station) and
a Level 2 (area) router.
Multiarea IS-IS: the first instance of the IS-IS routing process is a
Level 1-2 router. Remaining instances are Level 1 routers.
Default-information originate
Disabled.
Log IS-IS adjacency state changes.
Disabled.
LSP generation throttling timers
Maximum interval between two consecutive occurrences: 5 seconds.
Initial LSP generation delay: 50 ms.
Hold time between the first and second LSP generation: 5000 ms.
LSP maximum lifetime (without a
refresh)
1200 seconds (20 minutes) before t.he LSP packet is deleted.
LSP refresh interval
Send LSP refreshes every 900 seconds (15 minutes).
Maximum LSP packet size
1497 bytes.
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Enabling IS-IS Routing
Feature
Default Setting
NSF Awareness
Enabled. Allows Layer 3 Switches to continue forwarding packets
from a neighboring NSF-capable router during hardware or software
changes.
Partial route computation (PRC)
throttling timers
Maximum PRC wait interval: 5 seconds.
Initial PRC calculation delay after a topology change: 2000 ms.
Hold time between the first and second PRC calculation: 5000 ms.
Partition avoidance
Disabled.
Password
No area or domain password is defined, and authentication is
disabled.
Set-overload-bit
Disabled. When enabled, if no arguments are entered, the overload
bit is set immediately and remains set until you enter the no
set-overload-bit command.
Shortest path first (SPF) throttling
timers
Maximum interval between consecutive SFPs: 10 seconds.
Initial SFP calculation after a topology change: 5500 ms.
Holdtime between the first and second SFP calculation: 5500 ms.
Summary-address
Disabled.
Nonstop Forwarding Awareness
The integrated IS-IS NSF Awareness feature is supported for IPv4G. The feature allows customer premises
equipment (CPE) routers that are NSF-aware to help NSF-capable routers perform nonstop forwarding of
packets. The local router is not necessarily performing NSF, but its awareness of NSF allows the integrity
and accuracy of the routing database and link-state database on the neighboring NSF-capable router to be
maintained during the switchover process.
This feature is automatically enabled and requires no configuration. For more information on this feature, see
the Integrated IS-IS Nonstop Forwarding (NSF) Awareness Feature Guide.
Enabling IS-IS Routing
To enable IS-IS, you specify a name and NET for each routing process. You then enable IS-IS routing on the
interface and specify the area for each instance of the routing process.
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DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
Enables ISO connectionless routing on the switch.
clns routing
Example:
Switch(config)# clns routing
Step 3
router isis [area tag]
Enables the IS-IS routing for the specified routing process and enter
IS-IS routing configuration mode.
Example:
(Optional) Use the area tag argument to identify the area to which
the IS-IS router is assigned. You must enter a value if you are
configuring multiple IS-IS areas.
Switch(config)# router isis tag1
The first IS-IS instance configured is Level 1-2 by default. Later
instances are automatically Level 1. You can change the level of
routing by using the is-type global configuration command.
Step 4
net network-entity-title
Configures the NETs for the routing process. If you are configuring
multiarea IS-IS, specify a NET for each routing process. You can
specify a name for a NET and for an address.
Example:
Switch(config-router)# net
47.0004.004d.0001.0001.0c11.1111.00
Step 5
is-type {level-1 | level-1-2 | level-2-only}
Example:
(Optional) Configures the router to act as a Level 1 (station) router,
a Level 2 (area) router for multi-area routing, or both (the default):
• level-1—act as a station router only
Switch(config-router)# is-type
level-2-only
• level-1-2—act as both a station router and an area router
• level 2—act as an area router only
Step 6
Returns to global configuration mode.
exit
Example:
Switch(config-router)# end
Step 7
interface interface-id
Specifies an interface to route IS-IS, and enter interface configuration
mode. If the interface is not already configured as a Layer 3 interface,
enter the no switchport command to put it into Layer 3 mode.
Example:
Switch(config)# interface gigabitethernet
1/0/1
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Example: Configuring IS-IS Routing
Step 8
Command or Action
Purpose
ip router isis [area tag]
Configures an IS-IS routing process for ISO CLNS on the interface
and attach an area designator to the routing process.
Example:
Switch(config-if)# ip router isis tag1
Step 9
clns router isis [area tag]
Enables ISO CLNS on the interface.
Example:
Switch(config-if)# clns router isis tag1
Step 10
ip address ip-address-mask
Example:
Define the IP address for the interface. An IP address is required on
all interfaces in an area enabled for IS-IS if any one interface is
configured for IS-IS routing.
Switch(config-if)# ip address 10.0.0.5
255.255.255.0
Step 11
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 12
show isis [area tag] database detail
Verifies your entries.
Example:
Switch# show isis database detail
Step 13
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config
startup-config
Example: Configuring IS-IS Routing
This example shows how to configure three routers to run conventional IS-IS as an IP routing protocol. In
conventional IS-IS, all routers act as Level 1 and Level 2 routers (by default).
Router A:
Switch(config)# clns routing
Switch(config)# router isis
Switch(config-router)# net 49.0001.0000.0000.000a.00
Switch(config-router)# exit
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# ip router isis
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IS-IS Global Parameters
Switch(config-if)# clns router isis
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# ip router isis
Switch(config-if)# clns router isis
Switch(config-router)# exit
Router B:
Switch(config)# clns routing
Switch(config)# router isis
Switch(config-router)# net 49.0001.0000.0000.000b.00
Switch(config-router)# exit
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# ip router isis
Switch(config-if)# clns router isis
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# ip router isis
Switch(config-if)# clns router isis
Switch(config-router)# exit
Router C:
Switch(config)# clns routing
Switch(config)# router isis
Switch(config-router)# net 49.0001.0000.0000.000c.00
Switch(config-router)# exit
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# ip router isis
Switch(config-if)# clns router isis
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# ip router isis
Switch(config-if)# clns router isis
Switch(config-router)# exit
IS-IS Global Parameters
These are some optional IS-IS global parameters that you can configure:
• You can force a default route into an IS-IS routing domain by configuring a default route controlled by
a route map. You can also specify other filtering options configurable under a route map.
• You can configure the router to ignore IS-IS LSPs that are received with internal checksum errors or to
purge corrupted LSPs, which causes the initiator of the LSP to regenerate it.
• You can assign passwords to areas and domains.
• You can create aggregate addresses that are represented in the routing table by a summary address
(route-summarization). Routes learned from other routing protocols can also be summarized. The metric
used to advertise the summary is the smallest metric of all the specific routes.
• You can set an overload bit.
• You can configure the LSP refresh interval and the maximum time that an LSP can remain in the router
database without a refresh.
• You can set the throttling timers for LSP generation, shortest path first computation, and partial route
computation.
• You can configure the Switch to generate a log message when an IS-IS adjacency changes state (up or
down).
• If a link in the network has a maximum transmission unit (MTU) size of less than 1500 bytes, you can
lower the LSP MTU so that routing will still occur.
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Configuring IS-IS Global Parameters
• The partition avoidance router configuration command prevents an area from becoming partitioned when
full connectivity is lost among a Level1-2 border router, adjacent Level 1 routers, and end hosts.
Configuring IS-IS Global Parameters
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
clns routing
Enables ISO connectionless routing on the switch.
Example:
Switch(config)# clns routing
Step 3
router isis
Specifies the IS-IS routing protocol and enters router configuration mode.
Example:
Switch(config)# router isis
Step 4
default-information originate [route-map (Optional) Forces a default route into the IS-IS routing domain. If you
enter route-map map-name, the routing process generates the default route
map-name]
if the route map is satisfied.
Example:
Switch(config-router)#
default-information originate
route-map map1
Step 5
ignore-lsp-errors
Example:
(Optional) Configures the router to ignore LSPs with internal checksum
errors, instead of purging the LSPs. This command is enabled by default
(corrupted LSPs are dropped). To purge the corrupted LSPs, enter the no
ignore-lsp-errors router configuration command.
Switch(config-router)#
ignore-lsp-errors
Step 6
area-password password
(Optional Configures the area authentication password, which is inserted
in Level 1 (station router level) LSPs.
Example:
Switch(config-router)# area-password
1password
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Step 7
Command or Action
Purpose
domain-password password
(Optional) Configures the routing domain authentication password, which
is inserted in Level 2 (area router level) LSPs.
Example:
Switch(config-router)#
domain-password 2password
Step 8
summary-address address mask [level-1 | (Optional) Creates a summary of addresses for a given level.
level-1-2 | level-2]
Example:
Switch(config-router)#
summary-address 10.1.0.0 255.255.0.0
level-2
Step 9
set-overload-bit [on-startup {seconds |
wait-for-bgp}]
Example:
Switch(config-router)#
set-overload-bit on-startup
wait-for-bgp
(Optional) Sets an overload bit (a hippity bit) to allow other routers to
ignore the router in their shortest path first (SPF) calculations if the router
is having problems.
• (Optional) on-startup—sets the overload bit only on startup. If
on-startup is not specified, the overload bit is set immediately and
remains set until you enter the no set-overload-bit command. If
on-startup is specified, you must enter a number of seconds or
wait-for-bgp.
• seconds—When the on-startup keyword is configured, causes the
overload bit to be set upon system startup and remain set for this
number of seconds. The range is from 5 to 86400 seconds.
• wait-for-bgp—When the on-startup keyword is configured, causes
the overload bit to be set upon system startup and remain set until
BGP has converged. If BGP does not signal IS-IS that it is converged,
IS-IS will turn off the overload bit after 10 minutes.
Step 10
lsp-refresh-interval seconds
Example:
(Optional) Sets an LSP refresh interval in seconds. The range is from 1 to
65535 seconds. The default is to send LSP refreshes every 900 seconds
(15 minutes).
Switch(config-router)#
lsp-refresh-interval 1080
Step 11
max-lsp-lifetime seconds
(Optional) Sets the maximum time that LSP packets remain in the router
database without being refreshed. The range is from 1 to 65535 seconds.
The default is 1200 seconds (20 minutes). After the specified time interval,
the LSP packet is deleted.
Example:
Switch(config-router)#
max-lsp-lifetime 1000
Step 12
lsp-gen-interval [level-1 | level-2]
lsp-max-wait [lsp-initial-wait
lsp-second-wait]
(Optional) Sets the IS-IS LSP generation throttling timers:
• lsp-max-wait—the maximum interval (in seconds) between two
consecutive occurrences of an LSP being generated. The range is 1
to 120, the default is 5.
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Command or Action
Example:
Switch(config-router)#
lsp-gen-interval level-2 2 50 100
Step 13
Purpose
• lsp-initial-wait—the initial LSP generation delay (in milliseconds).
The range is 1 to 10000; the default is 50.
• lsp-second-wait—the hold time between the first and second LSP
generation (in milliseconds). The range is 1 to 10000; the default is
5000.
spf-interval [level-1 | level-2] spf-max-wait (Optional) Sets IS-IS shortest path first (SPF) throttling timers.
[spf-initial-wait spf-second-wait]
• spf-max-wait—the maximum interval between consecutive SFPs (in
seconds). The range is 1 to 120, the default is 10.
Example:
Switch(config-router)# spf-interval
level-2 5 10 20
• spf-initial-wait—the initial SFP calculation after a topology change
(in milliseconds). The range is 1 to 10000; the default is 5500.
• spf-second-wait—the holdtime between the first and second SFP
calculation (in milliseconds). The range is 1 to 10000; the default is
5500.
Step 14
prc-interval prc-max-wait [prc-initial-wait (Optional) Sets IS-IS partial route computation (PRC) throttling timers.
prc-second-wait]
• prc-max-wait—the maximum interval (in seconds) between two
consecutive PRC calculations. The range is 1 to 120; the default is
Example:
5.
Switch(config-router)# prc-interval
5 10 20
• prc-initial-wait—the initial PRC calculation delay (in milliseconds)
after a topology change. The range is 1 to 10,000; the default is 2000.
• prc-second-wait—the hold time between the first and second PRC
calculation (in milliseconds). The range is 1 to 10,000; the default
is 5000.
Step 15
log-adjacency-changes [all]
Example:
(Optional) Sets the router to log IS-IS adjacency state changes. Enter all
to include all changes generated by events that are not related to the
Intermediate System-to-Intermediate System Hellos, including End
System-to-Intermediate System PDUs and link state packets (LSPs).
Switch(config-router)#
log-adjacency-changes all
Step 16
lsp-mtu size
(Optional) Specifies the maximum LSP packet size in bytes. The range is
128 to 4352; the default is 1497 bytes.
Example:
Note
Switch(config-router)# lsp mtu 1560
Step 17
partition avoidance
Example:
If any link in the network has a reduced MTU size, you must
change the LSP MTU size on all routers in the network.
(Optional) Causes an IS-IS Level 1-2 border router to stop advertising the
Level 1 area prefix into the Level 2 backbone when full connectivity is
lost among the border router, all adjacent level 1 routers, and end hosts.
Switch(config-router)# partition
avoidance
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Step 18
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 19
Verifies your entries.
show clns
Example:
Switch# show clns
Step 20
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config
startup-config
IS-IS Interface Parameters
You can optionally configure certain interface-specific IS-IS parameters, independently from other attached
routers. However, if you change some values from the defaults, such as multipliers and time intervals, it makes
sense to also change them on multiple routers and interfaces. Most of the interface parameters can be configured
for level 1, level 2, or both.
These are some interface level parameters you can configure:
• The default metric on the interface, which is used as a value for the IS-IS metric and assigned when
there is no quality of service (QoS) routing performed.
• The hello interval (length of time between hello packets sent on the interface) or the default hello packet
multiplier used on the interface to determine the hold time sent in IS-IS hello packets. The hold time
determines how long a neighbor waits for another hello packet before declaring the neighbor down. This
determines how quickly a failed link or neighbor is detected so that routes can be recalculated. Change
the hello-multiplier in circumstances where hello packets are lost frequently and IS-IS adjacencies are
failing unnecessarily. You can raise the hello multiplier and lower the hello interval correspondingly to
make the hello protocol more reliable without increasing the time required to detect a link failure.
• Other time intervals:
◦Complete sequence number PDU (CSNP) interval. CSNPs are sent by the designated router to
maintain database synchronization
◦Retransmission interval. This is the time between retransmission of IS-IS LSPs for point-to-point
links.
◦IS-IS LSP retransmission throttle interval. This is the maximum rate (number of milliseconds
between packets) at which IS-IS LSPs are re-sent on point-to-point links This interval is different
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from the retransmission interval, which is the time between successive retransmissions of the same
LSP
• Designated router election priority, which allows you to reduce the number of adjacencies required on
a multiaccess network, which in turn reduces the amount of routing protocol traffic and the size of the
topology database.
• The interface circuit type, which is the type of adjacency desired for neighbors on the specified interface
• Password authentication for the interface
Configuring IS-IS Interface Parameters
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
interface interface-id
Example:
Specifies the interface to be configured and enter interface configuration
mode. If the interface is not already configured as a Layer 3 interface,
enter the no switchport command to put it into Layer 3 mode.
Switch(config)# interface
gigabitethernet 1/0/1
Step 3
isis metric default-metric [level-1 | level-2] (Optional) Configures the metric (or cost) for the specified interface. The
range is from 0 to 63. The default is 10. If no level is entered, the default
is to apply to both Level 1 and Level 2 routers.
Example:
Switch(config-if)# isis metric 15
Step 4
isis hello-interval {seconds | minimal}
[level-1 | level-2]
Example:
Switch(config-if)# isis hello-interval
minimal
(Optional) Specifies the length of time between hello packets sent by the
switch. By default, a value three times the hello interval seconds is
advertised as the holdtime in the hello packets sent. With smaller hello
intervals, topological changes are detected faster, but there is more routing
traffic.
• minimal—causes the system to compute the hello interval based on
the hello multiplier so that the resulting hold time is 1 second.
• seconds—the range is from 1 to 65535. The default is 10 seconds.
Step 5
isis hello-multiplier multiplier [level-1 |
level-2]
(Optional) Specifies the number of IS-IS hello packets a neighbor must
miss before the router should declare the adjacency as down. The range
is from 3 to 1000. The default is 3. Using a smaller hello-multiplier causes
fast convergence, but can result in more routing instability.
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Command or Action
Purpose
Example:
Switch(config-if)# isis
hello-multiplier 5
Step 6
isis csnp-interval seconds [level-1 | level-2] (Optional) Configures the IS-IS complete sequence number PDU (CSNP)
interval for the interface. The range is from 0 to 65535. The default is
10 seconds.
Example:
Switch(config-if)# isis csnp-interval
15
Step 7
isis retransmit-interval seconds
Example:
(Optional) Configures the number of seconds between retransmission of
IS-IS LSPs for point-to-point links. The value you specify should be an
integer greater than the expected round-trip delay between any two routers
on the network. The range is from 0 to 65535. The default is 5 seconds.
Switch(config-if)# isis
retransmit-interval 7
Step 8
isis retransmit-throttle-interval
milliseconds
Example:
(Optional) Configures the IS-IS LSP retransmission throttle interval, which
is the maximum rate (number of milliseconds between packets) at which
IS-IS LSPs will be re-sent on point-to-point links. The range is from 0 to
65535. The default is determined by the isis lsp-interval command.
Switch(config-if)# isis
retransmit-throttle-interval 4000
Step 9
isis priority value [level-1 | level-2]
(Optional) Configures the priority to use for designated router election.
The range is from 0 to 127. The default is 64.
Example:
Switch(config-if)# isis priority 50
Step 10
isis circuit-type {level-1 | level-1-2 |
level-2-only}
(Optional) Configures the type of adjacency desired for neighbors on the
specified interface (specify the interface circuit type).
• level-1—a Level 1 adjacency is established if there is at least one
area address common to both this node and its neighbors.
Example:
Switch(config-if)# isis circuit-type
level-1-2
• level-1-2—a Level 1 and 2 adjacency is established if the neighbor
is also configured as both Level 1 and Level 2 and there is at least
one area in common. If there is no area in common, a Level 2
adjacency is established. This is the default.
• level 2—a Level 2 adjacency is established. If the neighbor router
is a Level 1 router, no adjacency is established.
Step 11
isis password password [level-1 | level-2]
Example:
(Optional) Configures the authentication password for an interface. By
default, authentication is disabled. Specifying Level 1 or Level 2 enables
the password only for Level 1 or Level 2 routing, respectively. If you do
not specify a level, the default is Level 1 and Level 2.
Switch(config-if)# isis password
secret
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Monitoring and Maintaining ISO IGRP and IS-IS
Step 12
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 13
show clns interface interface-id
Verifies your entries.
Example:
Switch# show clns interface
gigabitethernet 1/0/1
Step 14
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config
startup-config
Monitoring and Maintaining ISO IGRP and IS-IS
You can remove all contents of a CLNS cache or remove information for a particular neighbor or route. You
can display specific CLNS or IS-IS statistics, such as the contents of routing tables, caches, and databases.
You can also display information about specific interfaces, filters, or neighbors.
The following table lists the privileged EXEC commands for clearing and displaying ISO CLNS and IS-IS
routing. For explanations of the display fields, see the Cisco IOS Apollo Domain, Banyan VINES, DECnet,
ISO CLNS and XNS Command Reference ,use the Cisco IOS command reference master index, or search
online.
Table 13: ISO CLNS and IS-IS Clear and Show Commands
Command
Purpose
clear clns cache
Clears and reinitializes the
CLNS routing cache.
clear clns es-neighbors
Removes end system (ES)
neighbor information from
the adjacency database.
clear clns is-neighbors
Removes intermediate system
(IS) neighbor information
from the adjacency database.
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Command
Purpose
clear clns neighbors
Removes CLNS neighbor
information from the
adjacency database.
clear clns route
Removes dynamically derived
CLNS routing information.
show clns
Displays information about
the CLNS network.
show clns cache
Displays the entries in the
CLNS routing cache.
show clns es-neighbors
Displays ES neighbor entries,
including the associated areas.
show clns filter-expr
Displays filter expressions.
show clns filter-set
Displays filter sets.
show clns interface [interface-id]
Displays the CLNS-specific
or ES-IS information about
each interface.
show clns neighbor
Displays information about
IS-IS neighbors.
show clns protocol
List the protocol-specific
information for each IS-IS or
ISO IGRP routing process in
this router.
show clns route
Displays all the destinations
to which this router knows
how to route CLNS packets.
show clns traffic
Displays information about
the CLNS packets this router
has seen.
show ip route isis
Displays the current state of
the ISIS IP routing table.
show isis database
Displays the IS-IS link-state
database.
show isis routes
Displays the IS-IS Level 1
routing table.
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Command
Purpose
show isis spf-log
Displays a history of the
shortest path first (SPF)
calculations for IS-IS.
show isis topology
Displays a list of all
connected routers in all areas.
show route-map
Displays all route maps
configured or only the one
specified.
trace clns destination
Discover the paths taken to a
specified destination by
packets in the network.
which-route {nsap-address | clns-name}
Displays the routing table in
which the specified CLNS
destination is found.
Information About Multi-VRF CE
Virtual Private Networks (VPNs) provide a secure way for customers to share bandwidth over an ISP backbone
network. A VPN is a collection of sites sharing a common routing table. A customer site is connected to the
service-provider network by one or more interfaces, and the service provider associates each interface with
a VPN routing table, called a VPN routing/forwarding (VRF) table.
The switch supports multiple VPN routing/forwarding (multi-VRF) instances in customer edge (CE) devices
(multi-VRF CE) when the it is running the IP services or advanced IP Services feature set. Multi-VRF CE
allows a service provider to support two or more VPNs with overlapping IP addresses.
Note
The switch does not use Multiprotocol Label Switching (MPLS) to support VPNs.
Understanding Multi-VRF CE
Multi-VRF CE is a feature that allows a service provider to support two or more VPNs, where IP addresses
can be overlapped among the VPNs. Multi-VRF CE uses input interfaces to distinguish routes for different
VPNs and forms virtual packet-forwarding tables by associating one or more Layer 3 interfaces with each
VRF. Interfaces in a VRF can be either physical, such as Ethernet ports, or logical, such as VLAN SVIs, but
an interface cannot belong to more than one VRF at any time.
Note
Multi-VRF CE interfaces must be Layer 3 interfaces.
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Understanding Multi-VRF CE
Multi-VRF CE includes these devices:
• Customer edge (CE) devices provide customers access to the service-provider network over a data link
to one or more provider edge routers. The CE device advertises the site’s local routes to the router and
learns the remote VPN routes from it. A switch can be a CE.
• Provider edge (PE) routers exchange routing information with CE devices by using static routing or a
routing protocol such as BGP, RIPv2, OSPF, or EIGRP. The PE is only required to maintain VPN routes
for those VPNs to which it is directly attached, eliminating the need for the PE to maintain all of the
service-provider VPN routes. Each PE router maintains a VRF for each of its directly connected sites.
Multiple interfaces on a PE router can be associated with a single VRF if all of these sites participate in
the same VPN. Each VPN is mapped to a specified VRF. After learning local VPN routes from CEs, a
PE router exchanges VPN routing information with other PE routers by using internal BGP (IBPG).
• Provider routers or core routers are any routers in the service provider network that do not attach to CE
devices.
With multi-VRF CE, multiple customers can share one CE, and only one physical link is used between the
CE and the PE. The shared CE maintains separate VRF tables for each customer and switches or routes packets
for each customer based on its own routing table. Multi-VRF CE extends limited PE functionality to a CE
device, giving it the ability to maintain separate VRF tables to extend the privacy and security of a VPN to
the branch office.
Network Topology
The figure shows a configuration using switches as multiple virtual CEs. This scenario is suited for customers
who have low bandwidth requirements for their VPN service, for example, small companies. In this case,
multi-VRF CE support is required in the switches. Because multi-VRF CE is a Layer 3 feature, each interface
in a VRF must be a Layer 3 interface.
Figure 7: Switches Acting as Multiple Virtual CEs
When the CE switch receives a command to add a Layer 3 interface to a VRF, it sets up the appropriate
mapping between the VLAN ID and the policy label (PL) in multi-VRF-CE-related data structures and adds
the VLAN ID and PL to the VLAN database.
When multi-VRF CE is configured, the Layer 3 forwarding table is conceptually partitioned into two sections:
• The multi-VRF CE routing section contains the routes from different VPNs.
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• The global routing section contains routes to non-VPN networks, such as the Internet.
VLAN IDs from different VRFs are mapped into different policy labels, which are used to distinguish the
VRFs during processing. For each new VPN route learned, the Layer 3 setup function retrieves the policy
label by using the VLAN ID of the ingress port and inserts the policy label and new route to the multi-VRF
CE routing section. If the packet is received from a routed port, the port internal VLAN ID number is used;
if the packet is received from an SVI, the VLAN number is used.
Packet-Forwarding Process
This is the packet-forwarding process in a multi-VRF-CE-enabled network:
• When the switch receives a packet from a VPN, the switch looks up the routing table based on the input
policy label number. When a route is found, the switch forwards the packet to the PE.
• When the ingress PE receives a packet from the CE, it performs a VRF lookup. When a route is found,
the router adds a corresponding MPLS label to the packet and sends it to the MPLS network.
• When an egress PE receives a packet from the network, it strips the label and uses the label to identify
the correct VPN routing table. Then it performs the normal route lookup. When a route is found, it
forwards the packet to the correct adjacency.
• When a CE receives a packet from an egress PE, it uses the input policy label to look up the correct
VPN routing table. If a route is found, it forwards the packet within the VPN.
Network Components
To configure VRF, you create a VRF table and specify the Layer 3 interface associated with the VRF. Then
configure the routing protocols in the VPN and between the CE and the PE. BGP is the preferred routing
protocol used to distribute VPN routing information across the provider’s backbone. The multi-VRF CE
network has three major components:
• VPN route target communities—lists of all other members of a VPN community. You need to configure
VPN route targets for each VPN community member.
• Multiprotocol BGP peering of VPN community PE routers—propagates VRF reachability information
to all members of a VPN community. You need to configure BGP peering in all PE routers within a
VPN community.
• VPN forwarding—transports all traffic between all VPN community members across a VPN
service-provider network.
VRF-Aware Services
IP services can be configured on global interfaces, and these services run within the global routing instance.
IP services are enhanced to run on multiple routing instances; they are VRF-aware. Any configured VRF in
the system can be specified for a VRF-aware service.
VRF-Aware services are implemented in platform-independent modules. VRF means multiple routing instances
in Cisco IOS. Each platform has its own limit on the number of VRFs it supports.
VRF-aware services have the following characteristics:
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• The user can ping a host in a user-specified VRF.
• ARP entries are learned in separate VRFs. The user can display Address Resolution Protocol (ARP)
entries for specific VRFs.
How to Configure Multi-VRF CE
Default Multi-VRF CE Configuration
Table 14: Default VRF Configuration
Feature
Default Setting
VRF
Disabled. No VRFs are defined.
Maps
No import maps, export maps, or route maps are defined.
VRF maximum routes
Fast Ethernet switches: 8000 Gigabit Ethernet switches: 12000.
Forwarding table
The default for an interface is the global routing table.
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Multi-VRF CE Configuration Guidelines
Multi-VRF CE Configuration Guidelines
Note
To use multi-VRF CE, you must have the IP services or advanced IP services feature set enabled on your
switch.
• A switch with multi-VRF CE is shared by multiple customers, and each customer has its own routing
table.
• Because customers use different VRF tables, the same IP addresses can be reused. Overlapped IP
addresses are allowed in different VPNs.
• Multi-VRF CE lets multiple customers share the same physical link between the PE and the CE.
Trunk ports with multiple VLANs separate packets among customers. Each customer has its own
VLAN.
• Multi-VRF CE does not support all MPLS-VRF functionality. It does not support label exchange,
LDP adjacency, or labeled packets.
• For the PE router, there is no difference between using multi-VRF CE or using multiple CEs. In
Figure 41-6, multiple virtual Layer 3 interfaces are connected to the multi-VRF CE device.
• The switch supports configuring VRF by using physical ports, VLAN SVIs, or a combination of
both. The SVIs can be connected through an access port or a trunk port.
• A customer can use multiple VLANs as long as they do not overlap with those of other customers.
A customer’s VLANs are mapped to a specific routing table ID that is used to identify the appropriate
routing tables stored on the switch.
• The switch supports one global network and up to 26 VRFs.
• Most routing protocols (BGP, OSPF, RIP, and static routing) can be used between the CE and the
PE. However, we recommend using external BGP (EBGP) for these reasons:
◦BGP does not require multiple algorithms to communicate with multiple CEs.
◦BGP is designed for passing routing information between systems run by different
administrations.
◦BGP makes it easy to pass attributes of the routes to the CE.
• Multi-VRF CE does not affect the packet switching rate.
• VPN multicast is not supported.
• You can enable VRF on a private VLAN, and the reverse.
• You cannot enable VRF when policy-based routing (PBR) is enabled on an interface, and the reverse.
• You cannot enable VRF when Web Cache Communication Protocol (WCCP) is enabled on an
interface, and the reverse.
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Configuring VRFs
For complete syntax and usage information for the commands, see the switch command reference for this
release and the Cisco IOS Switching Services Command Reference.
Note
On changing the VRF configuration on a stack switch, it is advised to reload the entire stack. This is
essential to maintain consistency between the CEF and the VRF control plane, and to avoid any error
messages being displayed due to inconsistency in case of a master switchover.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
Enables IP routing.
ip routing
Example:
Switch(config)# ip routing
Step 3
ip vrf vrf-name
Names the VRF, and enter VRF configuration mode.
Example:
Switch(config)# ip vrf vpn1
Step 4
rd route-distinguisher
Creates a VRF table by specifying a route distinguisher. Enter
either an AS number and an arbitrary number (xxx:y) or an IP
address and arbitrary number (A.B.C.D:y)
Example:
Switch(config-vrf)# rd 100:2
Step 5
route-target {export | import | both}
route-target-ext-community
Example:
Switch(config-vrf)# route-target both 100:2
Step 6
import map route-map
Creates a list of import, export, or import and export route
target communities for the specified VRF. Enter either an AS
system number and an arbitrary number (xxx:y) or an IP
address and an arbitrary number (A.B.C.D:y). The
route-target-ext-community should be the same as the
route-distinguisher entered in Step 4.
(Optional) Associates a route map with the VRF.
Example:
Switch(config-vrf)# import map importmap1
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Step 7
Command or Action
Purpose
interface interface-id
Specifies the Layer 3 interface to be associated with the VRF,
and enter interface configuration mode. The interface can be
a routed port or SVI.
Example:
Switch(config-vrf)# interface gigabitethernet
1/0/1
Step 8
ip vrf forwarding vrf-name
Associates the VRF with the Layer 3 interface.
Example:
Switch(config-if)# ip vrf forwarding vpn1
Step 9
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 10
show ip vrf [brief | detail | interfaces] [vrf-name]
Verifies the configuration. Displays information about the
configured VRFs.
Example:
Switch# show ip vrf interfaces vpn1
Step 11
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Configuring VRF-Aware Services
These services are VRF-Aware:
• ARP
• Ping
• Simple Network Management Protocol (SNMP)
• Unicast Reverse Path Forwarding (uRPF)
• Syslog
• Traceroute
• FTP and TFTP
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Note
The switch does not support VRF-aware services for Unicast Reverse Path Forwarding
(uRPF) or Network Time Protocol (NTP).
Configuring VRF-Aware Services for ARP
For complete syntax and usage information for the commands, see the switch command reference for this
release and the Cisco IOS Switching Services Command Reference, Release 12.4.
DETAILED STEPS
Step 1
Command or Action
Purpose
show ip arp vrf vrf-name
Displays the ARP table in the specified VRF.
Example:
Switch# show ip arp vrf vpn1
Configuring VRF-Aware Services for Ping
For complete syntax and usage information for the commands, see the switch command reference for this
release and the Cisco IOS Switching Services Command Reference, Release 12.4.
DETAILED STEPS
Step 1
Command or Action
Purpose
ping vrfvrf-nameip-host
Displays the ARP table in the specified VRF.
Example:
Switch# ping vrf vpn1 ip-host
Configuring VRF-Aware Services for SNMP
For complete syntax and usage information for the commands, refer to the switch command reference for this
release and the Cisco IOS Switching Services Command Reference, Release 12.4.
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DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
snmp-server trap authentication vrf
Enables SNMP traps for packets on a VRF.
Example:
Switch(config)# snmp-server trap authentication vrf
Step 3
snmp-server engineID remote host vrf vpn-instance engine-id Configures a name for the remote SNMP engine on
a switch.
string
Example:
Switch(config)# snmp-server engineID remote
172.16.20.3 vrf vpn1 80000009030000B064EFE100
Step 4
snmp-server host host vrf vpn-instance traps community
Example:
Specifies the recipient of an SNMP trap operation
and specifies the VRF table to be used for sending
SNMP traps.
Switch(config)# snmp-server host 172.16.20.3 vrf vpn1
traps comaccess
Step 5
snmp-server host host vrf vpn-instance informs community
Example:
Specifies the recipient of an SNMP inform operation
and specifies the VRF table to be used for sending
SNMP informs.
Switch(config)# snmp-server host 172.16.20.3 vrf vpn1
informs comaccess
Step 6
snmp-server user user group remote host vrf vpn-instance
security model
Adds a user to an SNMP group for a remote host on
a VRF for SNMP access.
Example:
Switch(config)# snmp-server user abcd remote
172.16.20.3 vrf vpn1 priv v2c 3des secure3des
Step 7
end
Returns to privileged EXEC mode.
Example:
Switch(config-if)# end
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Configuring VRF-Aware Services
Configuring VRF-Aware Servcies for HSRP
HSRP support for VRFs ensures that HSRP virtual IP addresses are added to the correct IP routing table.
For complete syntax and usage information for the commands, refer to the switch command reference for this
release and the Cisco IOS Switching Services Command Reference, Release 12.4.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
interfaceinterface-id
Enters interface configuration mode, and specifies the
Layer 3 interface to configure.
Example:
Switch(config)# interface gigabitethernet 1/0/1
Step 3
Removes the interface from Layer 2 configuration
mode if it is a physical interface.
no switchport
Example:
Switch(config-if)# no switchport
Step 4
ip vrf forwarding vrf-name
Configures VRF on the interface.
Example:
Switch(config-if)# ip vrf forwarding vpn1
Step 5
ip address ip-address
Enters the IP address for the interface.
Example:
Switch(config-if)# ip address 10.1.5.1
Step 6
standby 1 ip ip-address
Enables HSRP and configure the virtual IP address.
Example:
Switch(config-if)#standby 1 ip 10.1.1.254
Step 7
Returns to privileged EXEC mode.
end
Example:
Switch(config-if)# end
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Configuring VRF-Aware Services
Configuring VRF-Aware Servcies for uRPF
uRPF can be configured on an interface assigned to a VRF, and source lookup is done in the VRF table.
For complete syntax and usage information for the commands, refer to the switch command reference for this
release and the Cisco IOS Switching Services Command Reference, Release 12.4.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
interface interface-id
Enters interface configuration mode, and specifies
the Layer 3 interface to configure.
Example:
Switch(config)#
interface gigabitethernet 1/0/1
Step 3
no switchport
Removes the interface from Layer 2 configuration
mode if it is a physical interface.
Example:
Switch(config-if)# no switchport
Step 4
ip vrf forwarding vrf-name
Configures VRF on the interface.
Example:
Switch(config-if)# ip vrf forwarding vpn2
Step 5
ip address ip-address
Enters the IP address for the interface.
Example:
Switch(config-if)# ip address 10.1.5.1
Step 6
ip verify unicast reverse-path
Enables uRPF on the interface.
Example:
Switch(config-if)# ip verify unicast reverse-path
Step 7
end
Returns to privileged EXEC mode.
Example:
Switch(config-if)# end
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Configuring VRF-Aware Services
Configuring VRF-Aware RADIUS
To configure VRF-Aware RADIUS, you must first enable AAA on a RADIUS server. The switch supports
the ip vrf forwarding vrf-name server-group configuration and the ip radius source-interface global
configuration commands, as described in the Per VRF AAA Feature Guide.
Configuring VRF-Aware Services for Syslog
For complete syntax and usage information for the commands, refer to the switch command reference for this
release and the Cisco IOS Switching Services Command Reference, Release 12.4.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
Enables or temporarily disables logging of storage
router event message.
logging on
Example:
Switch(config)# logging on
Step 3
logging host ip-address vrf vrf-name
Specifies the host address of the syslog server where
logging messages are to be sent.
Example:
Switch(config)# logging host 10.10.1.0 vrf vpn1
Step 4
logging buffered logging buffered size debugging
Logs messages to an internal buffer.
Example:
Switch(config)# logging buffered critical 6000
debugging
Step 5
logging trap debugging
Limits the logging messages sent to the syslog server.
Example:
Switch(config)# logging trap debugging
Step 6
logging facility facility
Sends system logging messages to a logging facility.
Example:
Switch(config)# logging facility user
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Configuring VRF-Aware Services
Step 7
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config-if)# end
Configuring VRF-Aware Services for Traceroute
For complete syntax and usage information for the commands, refer to the switch command reference for this
release and the Cisco IOS Switching Services Command Reference, Release 12.4.
DETAILED STEPS
Step 1
Command or Action
Purpose
traceroute vrf vrf-name ipaddress
Specifies the name of a VPN VRF in which to find the
destination address.
Example:
Switch(config)# traceroute vrf vpn2 10.10.1.1
Configuring VRF-Aware Services for FTP and TFTP
So that FTP and TFTP are VRF-aware, you must configure some FTP/TFTP CLIs. For example, if you want
to use a VRF table that is attached to an interface, say E1/0, you need to configure the ip tftp source-interface
E1/0 or the ip ftp source-interface E1/0 command to inform TFTP or FTP server to use a specific routing
table. In this example, the VRF table is used to look up the destination IP address. These changes are
backward-compatible and do not affect existing behavior. That is, you can use the source-interface CLI to
send packets out a particular interface even if no VRF is configured on that interface.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
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Configuring Multicast VRFs
Step 2
Command or Action
Purpose
ip ftp source-interface interface-type interface-number
Specifies the source IP address for FTP
connections.
Example:
Switch(config)# ip ftp source-interface
gigabitethernet 1/0/2
Step 3
Returns to privileged EXEC mode.
end
Example:
Switch(config)#end
Step 4
Enters global configuration mode.
configure terminal
Example:
Switch# configure terminal
Step 5
ip tftp source-interface interface-type interface-number
Specifies the source IP address for TFTP
connections.
Example:
Switch(config)# ip tftp source-interface
gigabitethernet 1/0/2
Step 6
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 7
Returns to privileged EXEC mode.
end
Example:
Switch(config)#end
Configuring Multicast VRFs
For complete syntax and usage information for the commands, see the switch command reference for this
release and the Cisco IOS IP Multicast Command Reference.
For more information about configuring a multicast within a Multi-VRF CE, see the IP Routing:
Protocol-Independent Configuration Guide, Cisco IOS Release 15S.
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Configuring Multicast VRFs
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
ip routing
Enables IP routing mode.
Example:
Switch(config)# ip routing
Step 3
ip vrf vrf-name
Names the VRF, and enter VRF configuration mode.
Example:
Switch(config)# ip vrf vpn1
Step 4
rd route-distinguisher
Example:
Creates a VRF table by specifying a route distinguisher.
Enter either an AS number and an arbitrary number (xxx:y)
or an IP address and an arbitrary number (A.B.C.D:y)
Switch(config-vrf)# rd 100:2
Step 5
route-target {export | import | both}
route-target-ext-community
Example:
Switch(config-vrf)# route-target import 100:2
Step 6
import map route-map
Creates a list of import, export, or import and export route
target communities for the specified VRF. Enter either an
AS system number and an arbitrary number (xxx:y) or an
IP address and an arbitrary number (A.B.C.D:y). The
route-target-ext-community should be the same as the
route-distinguisher entered in Step 4.
(Optional) Associates a route map with the VRF.
Example:
Switch(config-vrf)# import map importmap1
Step 7
ip multicast-routing vrf vrf-name distributed
(Optional) Enables global multicast routing for VRF table.
Example:
Switch(config-vrf)# ip multicast-routing vrf
vpn1 distributed
Step 8
interface interface-id
Example:
Specifies the Layer 3 interface to be associated with the
VRF, and enter interface configuration mode. The interface
can be a routed port or an SVI.
Switch(config-vrf)# interface gigabitethernet
1/0/2
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Configuring a VPN Routing Session
Step 9
Command or Action
Purpose
ip vrf forwarding vrf-name
Associates the VRF with the Layer 3 interface.
Example:
Switch(config-if)# ip vrf forwarding vpn1
Step 10
ip address ip-address mask
Configures IP address for the Layer 3 interface.
Example:
Switch(config-if)# ip address 10.1.5.1
255.255.255.0
Step 11
ip pim sparse-dense mode
Enables PIM on the VRF-associated Layer 3 interface.
Example:
Switch(config-if)# ip pim sparse-dense mode
Step 12
Returns to privileged EXEC mode.
end
Example:
Switch(config)# end
Step 13
show ip vrf [brief | detail | interfaces] [vrf-name]
Verifies the configuration. Displays information about the
configured VRFs.
Example:
Switch# show ip vrf detail vpn1
Step 14
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Configuring a VPN Routing Session
Routing within the VPN can be configured with any supported routing protocol (RIP, OSPF, EIGRP, or BGP)
or with static routing. The configuration shown here is for OSPF, but the process is the same for other protocols.
Note
To configure an EIGRP routing process to run within a VRF instance, you must configure an
autonomous-system number by entering the autonomous-system autonomous-system-number
address-family configuration mode command.
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Configuring a VPN Routing Session
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
router ospf process-id vrf vrf-name
Enables OSPF routing, specifies a VPN forwarding table,
and enter router configuration mode.
Example:
Switch(config)# router ospf 1 vrf vpn1
Step 3
log-adjacency-changes
(Optional) Logs changes in the adjacency state. This is
the default state.
Example:
Switch(config-router)# log-adjacency-changes
Step 4
redistribute bgp autonomous-system-number subnets
Sets the switch to redistribute information from the BGP
network to the OSPF network.
Example:
Switch(config-router)# redistribute bgp 10
subnets
Step 5
network network-number area area-id
Defines a network address and mask on which OSPF
runs and the area ID for that network address.
Example:
Switch(config-router)# network 1 area 2
Step 6
end
Returns to privileged EXEC mode.
Example:
Switch(config-router)# end
Step 7
show ip ospf process-id
Verifies the configuration of the OSPF network.
Example:
Switch# show ip ospf 1
Step 8
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
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Configuring BGP PE to CE Routing Sessions
Configuring BGP PE to CE Routing Sessions
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
router bgp autonomous-system-number
Example:
Configures the BGP routing process with the AS
number passed to other BGP routers, and enter router
configuration mode.
Switch(config)# router bgp 2
Step 3
network network-number mask network-mask
Specifies a network and mask to announce using BGP.
Example:
Switch(config-router)# network 5 mask 255.255.255.0
Step 4
redistribute ospf process-id match internal
Sets the switch to redistribute OSPF internal routes.
Example:
Switch(config-router)# redistribute ospf 1 match
internal
Step 5
network network-number area area-id
Defines a network address and mask on which OSPF
runs and the area ID for that network address.
Example:
Switch(config-router)# network 5 area 2
Step 6
address-family ipv4 vrf vrf-name
Defines BGP parameters for PE to CE routing
sessions, and enter VRF address-family mode.
Example:
Switch(config-router)# address-family ipv4 vrf vpn1
Step 7
neighbor address remote-as as-number
Defines a BGP session between PE and CE routers.
Example:
Switch(config-router)# neighbor 10.1.1.2 remote-as
2
Step 8
neighbor address activate
Activates the advertisement of the IPv4 address family.
Example:
Switch(config-router)# neighbor 10.2.1.1 activate
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Step 9
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config-router)# end
Step 10
show ip bgp [ipv4] [neighbors]
Verifies BGP configuration.
Example:
Switch# show ip bgp ipv4 neighbors
Step 11
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Multi-VRF CE Configuration Example
OSPF is the protocol used in VPN1, VPN2, and the global network. BGP is used in the CE to PE connections.
The examples following the illustration show how to configure a switch as CE Switch A, and the VRF
configuration for customer switches D and F. Commands for configuring CE Switch C and the other customer
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Multi-VRF CE Configuration Example
switches are not included but would be similar. The example also includes commands for configuring traffic
to Switch A for a Catalyst 6000 or Catalyst 6500 switch acting as a PE router.
Figure 8: Multi-VRF CE Configuration Example
On Switch A, enable routing and configure VRF.
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# ip routing
Switch(config)# ip vrf v11
Switch(config-vrf)# rd 800:1
Switch(config-vrf)# route-target export 800:1
Switch(config-vrf)# route-target import 800:1
Switch(config-vrf)# exit
Switch(config)# ip vrf v12
Switch(config-vrf)# rd 800:2
Switch(config-vrf)# route-target export 800:2
Switch(config-vrf)# route-target import 800:2
Switch(config-vrf)# exit
Configure the loopback and physical interfaces on Switch A. Gigabit Ethernet port 1 is a trunk connection to
the PE. Gigabit Ethernet ports 8 and 11 connect to VPNs:
Switch(config)# interface loopback1
Switch(config-if)# ip vrf forwarding v11
Switch(config-if)# ip address 8.8.1.8 255.255.255.0
Switch(config-if)# exit
Switch(config)# interface loopback2
Switch(config-if)# ip vrf forwarding v12
Switch(config-if)# ip address 8.8.2.8 255.255.255.0
Switch(config-if)# exit
Switch(config)# interface gigabitethernet1/0/5
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Switch(config-if)# switchport trunk encapsulation dot1q
Switch(config-if)# switchport mode trunk
Switch(config-if)# no ip address
Switch(config-if)# exit
Switch(config)# interface gigabitethernet1/0/8
Switch(config-if)# switchport access vlan 208
Switch(config-if)# no ip address
Switch(config-if)# exit
Switch(config)# interface gigabitethernet1/0/11
Switch(config-if)# switchport trunk encapsulation dot1q
Switch(config-if)# switchport mode trunk
Switch(config-if)# no ip address
Switch(config-if)# exit
Configure the VLANs used on Switch A. VLAN 10 is used by VRF 11 between the CE and the PE. VLAN
20 is used by VRF 12 between the CE and the PE. VLANs 118 and 208 are used for the VPNs that include
Switch F and Switch D, respectively:
Switch(config)# interface vlan10
Switch(config-if)# ip vrf forwarding v11
Switch(config-if)# ip address 38.0.0.8 255.255.255.0
Switch(config-if)# exit
Switch(config)# interface vlan20
Switch(config-if)# ip vrf forwarding v12
Switch(config-if)# ip address 83.0.0.8 255.255.255.0
Switch(config-if)# exit
Switch(config)# interface vlan118
Switch(config-if)# ip vrf forwarding v12
Switch(config-if)# ip address 118.0.0.8 255.255.255.0
Switch(config-if)# exit
Switch(config)# interface vlan208
Switch(config-if)# ip vrf forwarding v11
Switch(config-if)# ip address 208.0.0.8 255.255.255.0
Switch(config-if)# exit
Configure OSPF routing in VPN1 and VPN2.
Switch(config)# router
Switch(config-router)#
Switch(config-router)#
Switch(config-router)#
Switch(config)# router
Switch(config-router)#
Switch(config-router)#
Switch(config-router)#
ospf 1 vrf vl1
redistribute bgp 800 subnets
network 208.0.0.0 0.0.0.255 area 0
exit
ospf 2 vrf vl2
redistribute bgp 800 subnets
network 118.0.0.0 0.0.0.255 area 0
exit
Configure BGP for CE to PE routing.
Switch(config)# router bgp 800
Switch(config-router)# address-family ipv4 vrf vl2
Switch(config-router-af)# redistribute ospf 2 match internal
Switch(config-router-af)# neighbor 83.0.0.3 remote-as 100
Switch(config-router-af)# neighbor 83.0.0.3 activate
Switch(config-router-af)# network 8.8.2.0 mask 255.255.255.0
Switch(config-router-af)# exit
Switch(config-router)# address-family ipv4 vrf vl1
Switch(config-router-af)# redistribute ospf 1 match internal
Switch(config-router-af)# neighbor 38.0.0.3 remote-as 100
Switch(config-router-af)# neighbor 38.0.0.3 activate
Switch(config-router-af)# network 8.8.1.0 mask 255.255.255.0
Switch(config-router-af)# end
Switch D belongs to VPN 1. Configure the connection to Switch A by using these commands.
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# ip routing
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# no switchport
Switch(config-if)# ip address 208.0.0.20 255.255.255.0
Switch(config-if)# exit
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Switch(config)# router ospf 101
Switch(config-router)# network 208.0.0.0 0.0.0.255 area 0
Switch(config-router)# end
Switch F belongs to VPN 2. Configure the connection to Switch A by using these commands.
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# ip routing
Switch(config)# interface gigabitethernet1/0/1
Switch(config-if)# switchport trunk encapsulation dot1q
Switch(config-if)# switchport mode trunk
Switch(config-if)# no ip address
Switch(config-if)# exit
Switch(config)# interface vlan118
Switch(config-if)# ip address 118.0.0.11 255.255.255.0
Switch(config-if)# exit
Switch(config)# router ospf 101
Switch(config-router)# network 118.0.0.0 0.0.0.255 area 0
Switch(config-router)# end
When used on switch B (the PE router), these commands configure only the connections to the CE device,
Switch A.
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# ip vrf v1
Router(config-vrf)# rd 100:1
Router(config-vrf)# route-target export 100:1
Router(config-vrf)# route-target import 100:1
Router(config-vrf)# exit
Router(config)# ip vrf v2
Router(config-vrf)# rd 100:2
Router(config-vrf)# route-target export 100:2
Router(config-vrf)# route-target import 100:2
Router(config-vrf)# exit
Router(config)# ip cef
Router(config)# interface Loopback1
Router(config-if)# ip vrf forwarding v1
Router(config-if)# ip address 3.3.1.3 255.255.255.0
Router(config-if)# exit
Router(config)# interface Loopback2
Router(config-if)# ip vrf forwarding v2
Router(config-if)# ip address 3.3.2.3 255.255.255.0
Router(config-if)# exit
Router(config)# interface gigabitethernet1/1/0.10
Router(config-if)# encapsulation dot1q 10
Router(config-if)# ip vrf forwarding v1
Router(config-if)# ip address 38.0.0.3 255.255.255.0
Router(config-if)# exit
Router(config)# interface gigabitethernet1/1/0.20
Router(config-if)# encapsulation dot1q 20
Router(config-if)# ip vrf forwarding v2
Router(config-if)# ip address 83.0.0.3 255.255.255.0
Router(config-if)# exit
Router(config)# router bgp 100
Router(config-router)# address-family ipv4 vrf v2
Router(config-router-af)# neighbor 83.0.0.8 remote-as 800
Router(config-router-af)# neighbor 83.0.0.8 activate
Router(config-router-af)# network 3.3.2.0 mask 255.255.255.0
Router(config-router-af)# exit
Router(config-router)# address-family ipv4 vrf vl
Router(config-router-af)# neighbor 38.0.0.8 remote-as 800
Router(config-router-af)# neighbor 38.0.0.8 activate
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Router(config-router-af)# network 3.3.1.0 mask 255.255.255.0
Router(config-router-af)# end
Monitoring Multi-VRF CE
Table 15: Commands for Displaying Multi-VRF CE Information
show ip protocols vrf vrf-name
Displays routing protocol information
associated with a VRF.
Displays IP routing table information
show ip route vrf vrf-name [connected] [protocol
[as-number]] [list] [mobile] [odr] [profile] [static] [summary] associated with a VRF.
[supernets-only]
show ip vrf [brief | detail | interfaces] [vrf-name]
Displays information about the defined VRF
instances.
For more information about the information in the displays, see the Cisco IOS Switching Services Command
Reference, Release 12.4.
Configuring Unicast Reverse Path Forwarding
The unicast reverse path forwarding (unicast RPF) feature helps to mitigate problems that are caused by the
introduction of malformed or forged (spoofed) IP source addresses into a network by discarding IP packets
that lack a verifiable IP source address. For example, a number of common types of denial-of-service (DoS)
attacks, including Smurf and Tribal Flood Network (TFN), can take advantage of forged or rapidly changing
source IP addresses to allow attackers to thwart efforts to locate or filter the attacks. For Internet service
providers (ISPs) that provide public access, Unicast RPF deflects such attacks by forwarding only packets
that have source addresses that are valid and consistent with the IP routing table. This action protects the
network of the ISP, its customer, and the rest of the Internet.
Note
• Unicast RPF is supported in .
For detailed IP unicast RPF configuration information, see the Other Security Features chapter in the Cisco
IOS Security Configuration Guide.
Protocol-Independent Features
This section describes IP routing protocol-independent features that are available on switches running the
feature set . For a complete description of the IP routing protocol-independent commands in this chapter, see
the “IP Routing Protocol-Independent Commands” chapter of the Cisco IOS IP Command Reference, Volume
2 of 3: Routing Protocols.
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Distributed Cisco Express Forwarding
Distributed Cisco Express Forwarding
Information About Cisco Express Forwarding
Cisco Express Forwarding (CEF) is a Layer 3 IP switching technology used to optimize network performance.
CEF implements an advanced IP look-up and forwarding algorithm to deliver maximum Layer 3 switching
performance. CEF is less CPU-intensive than fast switching route caching, allowing more CPU processing
power to be dedicated to packet forwarding. In a switch stack, the hardware uses distributed CEF (dCEF) in
the stack. In dynamic networks, fast switching cache entries are frequently invalidated because of routing
changes, which can cause traffic to be process switched using the routing table, instead of fast switched using
the route cache. CEF and dCEF use the Forwarding Information Base (FIB) lookup table to perform
destination-based switching of IP packets.
The two main components in CEF and dCEF are the distributed FIB and the distributed adjacency tables.
• The FIB is similar to a routing table or information base and maintains a mirror image of the forwarding
information in the IP routing table. When routing or topology changes occur in the network, the IP
routing table is updated, and those changes are reflected in the FIB. The FIB maintains next-hop address
information based on the information in the IP routing table. Because the FIB contains all known routes
that exist in the routing table, CEF eliminates route cache maintenance, is more efficient for switching
traffic, and is not affected by traffic patterns.
• Nodes in the network are said to be adjacent if they can reach each other with a single hop across a link
layer. CEF uses adjacency tables to prepend Layer 2 addressing information. The adjacency table
maintains Layer 2 next-hop addresses for all FIB entries.
Because the switch or switch stack uses Application Specific Integrated Circuits (ASICs) to achieve
Gigabit-speed line rate IP traffic, CEF or dCEF forwarding applies only to the software-forwarding path, that
is, traffic that is forwarded by the CPU.
How to Configure Cisco Express Forwarding
CEF or distributed CEF is enabled globally by default. If for some reason it is disabled, you can re-enable it
by using the ip cef or ip cef distributed global configuration command.
The default configuration is CEF or dCEF enabled on all Layer 3 interfaces. Entering the no ip route-cache
cef interface configuration command disables CEF for traffic that is being forwarded by software. This
command does not affect the hardware forwarding path. Disabling CEF and using the debug ip packet detail
privileged EXEC command can be useful to debug software-forwarded traffic. To enable CEF on an interface
for the software-forwarding path, use the ip route-cache cef interface configuration command.
Caution
Although the no ip route-cache cef interface configuration command to disable CEF on an interface is
visible in the CLI, we strongly recommend that you do not disable CEF or dCEF on interfaces except for
debugging purposes.
To enable CEF or dCEF globally and on an interface for software-forwarded traffic if it has been disabled:
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SUMMARY STEPS
1. configure terminal
2. ip cef
3. ip cef distributed
4. interface interface-id
5. ip route-cache cef
6. end
7. show ip cef
8. show cef linecard [detail]
9. show cef linecard [slot-number] [detail]
10. show cef interface [interface-id]
11. show adjacency
12. copy running-config startup-config
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 2
ip cef
Enables CEF operation on a non-stacking switch.
Go to Step 4.
Example:
Switch(config)# ip cef
Step 3
ip cef distributed
Enables CEF operation on a active switch.
Example:
Switch(config)# ip cef distributed
Step 4
interface interface-id
Enters interface configuration mode, and specifies the Layer
3 interface to configure.
Example:
Switch(config)# interface gigabitethernet
1/0/1
Step 5
ip route-cache cef
Enables CEF on the interface for software-forwarded traffic.
Example:
Switch(config-if)# ip route-cache cef
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Number of Equal-Cost Routing Paths
Step 6
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config-if)# end
Step 7
Displays the CEF status on all interfaces.
show ip cef
Example:
Switch# show ip cef
Step 8
show cef linecard [detail]
(Optional) Displays CEF-related interface information on
a non-stacking switch.
Example:
Switch# show cef linecard detail
Step 9
show cef linecard [slot-number] [detail]
Example:
Switch# show cef linecard 5 detail
Step 10
show cef interface [interface-id]
(Optional) Displays CEF-related interface information on
a switch by stack member for all switches in the stack or
for the specified switch.
(Optional) For slot-number, enter the stack member switch
number.
Displays detailed CEF information for all interfaces or the
specified interface.
Example:
Switch# show cef interface gigabitethernet
1/0/1
Step 11
Displays CEF adjacency table information.
show adjacency
Example:
Switch# show adjacency
Step 12
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Number of Equal-Cost Routing Paths
Information About Equal-Cost Routing Paths
When a router has two or more routes to the same network with the same metrics, these routes can be thought
of as having an equal cost. The term parallel path is another way to see occurrences of equal-cost routes in a
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routing table. If a router has two or more equal-cost paths to a network, it can use them concurrently. Parallel
paths provide redundancy in case of a circuit failure and also enable a router to load balance packets over the
available paths for more efficient use of available bandwidth. Equal-cost routes are supported across switches
in a stack.
Even though the router automatically learns about and configures equal-cost routes, you can control the
maximum number of parallel paths supported by an IP routing protocol in its routing table. Although the
switch software allows a maximum of 32 equal-cost routes, the switch hardware will never use more than 16
paths per route.
How to Configure Equal-Cost Routing Paths
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
router {rip | ospf | eigrp}
Enters router configuration mode.
Example:
Switch(config)# router eigrp
Step 3
maximum-paths maximum
Example:
Sets the maximum number of parallel paths for the
protocol routing table. The range is from 1 to 16; the
default is 4 for most IP routing protocols, but only 1 for
BGP.
Switch(config-router)# maximum-paths 2
Step 4
end
Returns to privileged EXEC mode.
Example:
Switch(config-router)# end
Step 5
show ip protocols
Verifies the setting in the Maximum path field.
Example:
Switch# show ip protocols
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
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Static Unicast Routes
Static Unicast Routes
Information About Static Unicast Routes
Static unicast routes are user-defined routes that cause packets moving between a source and a destination to
take a specified path. Static routes can be important if the router cannot build a route to a particular destination
and are useful for specifying a gateway of last resort to which all unroutable packets are sent.
Switches running the LAN Base image support 16 user-configured static routes on SVIs. Static routing
configuration is supported on the LAN Base image only with the default SDM template and only on SVI
interfaces. No routing protocols are supported.
The switch retains static routes until you remove them. However, you can override static routes with dynamic
routing information by assigning administrative distance values. Each dynamic routing protocol has a default
administrative distance, as listed in Table 41-16. If you want a static route to be overridden by information
from a dynamic routing protocol, set the administrative distance of the static route higher than that of the
dynamic protocol.
Table 16: Dynamic Routing Protocol Default Administrative Distances
Route Source
Default Distance
Connected interface
0
Static route
1
Enhanced IRGP summary route
5
External BGP
20
Internal Enhanced IGRP
90
IGRP
100
OSPF
110
Internal BGP
200
Unknown
225
Static routes that point to an interface are advertised through RIP, IGRP, and other dynamic routing protocols,
whether or not static redistribute router configuration commands were specified for those routing protocols.
These static routes are advertised because static routes that point to an interface are considered in the routing
table to be connected and hence lose their static nature. However, if you define a static route to an interface
that is not one of the networks defined in a network command, no dynamic routing protocols advertise the
route unless a redistribute static command is specified for these protocols.
When an interface goes down, all static routes through that interface are removed from the IP routing table.
When the software can no longer find a valid next hop for the address specified as the forwarding router's
address in a static route, the static route is also removed from the IP routing table.
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Configuring Static Unicast Routes
Static unicast routes are user-defined routes that cause packets moving between a source and a destination to
take a specified path. Static routes can be important if the router cannot build a route to a particular destination
and are useful for specifying a gateway of last resort to which all unroutable packets are sent.
Follow these steps to configure a static route:
DETAILED STEPS
Step 1
Command or Action
Purpose
enable
Enables privileged EXEC mode. Enter your password
if prompted.
Example:
Switch> enable
Step 2
configure terminal
Enters the global configuration mode.
Example:
Switch# configure terminal
Step 3
ip route prefix mask {address | interface} [distance]
Establish a static route.
Example:
Switch(config)# ip route prefix mask
gigabitethernet 1/0/4
Step 4
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 5
show ip route
Displays the current state of the routing table to verify
the configuration.
Example:
Switch# show ip route
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
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Default Routes and Networks
What to Do Next
Use the no ip route prefix mask {address| interface} global configuration command to remove a static route.
The switch retains static routes until you remove them.
Default Routes and Networks
Information About Default Routes and Networks
A router might not be able to learn the routes to all other networks. To provide complete routing capability,
you can use some routers as smart routers and give the remaining routers default routes to the smart router.
(Smart routers have routing table information for the entire internetwork.) These default routes can be
dynamically learned or can be configured in the individual routers. Most dynamic interior routing protocols
include a mechanism for causing a smart router to generate dynamic default information that is then forwarded
to other routers.
If a router has a directly connected interface to the specified default network, the dynamic routing protocols
running on that device generate a default route. In RIP, it advertises the pseudonetwork 0.0.0.0.
A router that is generating the default for a network also might need a default of its own. One way a router
can generate its own default is to specify a static route to the network 0.0.0.0 through the appropriate device.
When default information is passed through a dynamic routing protocol, no further configuration is required.
The system periodically scans its routing table to choose the optimal default network as its default route. In
IGRP networks, there might be several candidate networks for the system default. Cisco routers use
administrative distance and metric information to set the default route or the gateway of last resort.
If dynamic default information is not being passed to the system, candidates for the default route are specified
with the ip default-network global configuration command. If this network appears in the routing table from
any source, it is flagged as a possible choice for the default route. If the router has no interface on the default
network, but does have a path to it, the network is considered as a possible candidate, and the gateway to the
best default path becomes the gateway of last resort.
How to Configure Default Routes and Networks
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
ip default-network network number
Specifies a default network.
Example:
Switch(config)# ip default-network 1
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Step 3
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 4
show ip route
Displays the selected default route in the gateway of
last resort display.
Example:
Switch# show ip route
Step 5
copy running-config startup-config
(Optional) Saves your entries in the configuration
file.
Example:
Switch# copy running-config startup-config
Route Maps to Redistribute Routing Information
Information About Route Maps
The switch can run multiple routing protocols simultaneously, and it can redistribute information from one
routing protocol to another. Redistributing information from one routing protocol to another applies to all
supported IP-based routing protocols.
You can also conditionally control the redistribution of routes between routing domains by defining enhanced
packet filters or route maps between the two domains. The match and set route-map configuration commands
define the condition portion of a route map. The match command specifies that a criterion must be matched.
The set command specifies an action to be taken if the routing update meets the conditions defined by the
match command. Although redistribution is a protocol-independent feature, some of the match and set
route-map configuration commands are specific to a particular protocol.
One or more match commands and one or more set commands follow a route-map command. If there are
no match commands, everything matches. If there are no set commands, nothing is done, other than the match.
Therefore, you need at least one match or set command.
Note
A route map with no set route-map configuration commands is sent to the CPU, which causes high CPU
utilization.
You can also identify route-map statements as permit or deny. If the statement is marked as a deny, the
packets meeting the match criteria are sent back through the normal forwarding channels (destination-based
routing). If the statement is marked as permit, set clauses are applied to packets meeting the match criteria.
Packets that do not meet the match criteria are forwarded through the normal routing channel.
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Related Topics
Information About Policy-Based Routing, on page 152
Other OSPF Parameters, on page 51
How to Configure a Route Map
Although each of Steps 3 through 14 in the following section is optional, you must enter at least one match
route-map configuration command and one set route-map configuration command.
Note
The keywords are the same as defined in the procedure to control the route distribution.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
route-mapmap-tag [permit | deny] [sequence
number]
Example:
Switch(config)# route-map rip-to-ospf permit
4
Defines any route maps used to control redistribution and enter
route-map configuration mode.
map-tag—A meaningful name for the route map. The
redistribute router configuration command uses this name to
reference this route map. Multiple route maps might share the
same map tag name.
(Optional) If permit is specified and the match criteria are met
for this route map, the route is redistributed as controlled by the
set actions. If deny is specified, the route is not redistributed.
sequence number (Optional)— Number that indicates the
position a new route map is to have in the list of route maps
already configured with the same name.
Step 3
match as-path path-list-number
Matches a BGP AS path access list.
Example:
Switch(config-route-map)#match as-path 10
Step 4
match community-list community-list-number
[exact]
Matches a BGP community list.
Example:
Switch(config-route-map)# match
community-list 150
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Step 5
Command or Action
Purpose
match ip address {access-list-number |
access-list-name} [...access-list-number |
...access-list-name]
Matches a standard access list by specifying the name or
number. It can be an integer from 1 to 199.
Example:
Switch(config-route-map)# match ip address 5
80
Step 6
match metric metric-value
Matches the specified route metric. The metric-value can be an
EIGRP metric with a specified value from 0 to 4294967295.
Example:
Switch(config-route-map)# match metric 2000
Step 7
match ip next-hop {access-list-number |
access-list-name} [...access-list-number |
...access-list-name]
Matches a next-hop router address passed by one of the access
lists specified (numbered from 1 to 199).
Example:
Switch(config-route-map)# match ip next-hop
8 45
Step 8
match tag tag value [...tag-value]
Matches the specified tag value in a list of one or more route
tag values. Each can be an integer from 0 to 4294967295.
Example:
Switch(config-route-map)# match tag 3500
Step 9
match interfacetype number [...type-number]
Matches the specified next hop route out one of the specified
interfaces.
Example:
Switch(config-route-map)# match interface
gigabitethernet 1/0/1
Step 10
match ip route-source {access-list-number |
access-list-name} [...access-list-number |
...access-list-name]
Matches the address specified by the specified advertised access
lists.
Example:
Switch(config-route-map)# match ip
route-source 10 30
Step 11
match route-type {local | internal | external [type-1 Matches the specified route-type:
| type-2]}
• local—Locally generated BGP routes.
Example:
Switch(config-route-map)# match route-type
local
• internal—OSPF intra-area and interarea routes or EIGRP
internal routes.
• external—OSPF external routes (Type 1 or Type 2) or
EIGRP external routes.
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Step 12
Command or Action
Purpose
set dampening halflife reuse suppress
max-suppress-time
Sets BGP route dampening factors.
Example:
Switch(config-route-map)# set dampening 30
1500 10000 120
Step 13
set local-preference value
Assigns a value to a local BGP path.
Example:
Switch(config-route-map)# set
local-preference 100
Step 14
set origin {igp | egp as | incomplete}
Sets the BGP origin code.
Example:
Switch(config-route-map)#set origin igp
Step 15
set as-path {tag | prepend as-path-string}
Modifies the BGP autonomous system path.
Example:
Switch(config-route-map)# set as-path tag
Step 16
set level {level-1 | level-2 | level-1-2 | stub-area |
backbone}
Sets the level for routes that are advertised into the specified
area of the routing domain. The stub-area and backbone are
OSPF NSSA and backbone areas.
Example:
Switch(config-route-map)# set level level-1-2
Step 17
set metric metric value
Sets the metric value to give the redistributed routes (for EIGRP
only). The metric value is an integer from -294967295 to
294967295.
Example:
Switch(config-route-map)# set metric 100
Step 18
set metricbandwidth delay reliability loading mtu
Example:
Switch(config-route-map)# set metric 10000
10 255 1 1500
Sets the metric value to give the redistributed routes (for EIGRP
only):
• bandwidth—Metric value or IGRP bandwidth of the route
in kilobits per second in the range 0 to 4294967295
• delay—Route delay in tens of microseconds in the range
0 to 4294967295.
• reliability—Likelihood of successful packet transmission
expressed as a number between 0 and 255, where 255
means 100 percent reliability and 0 means no reliability.
• loading—Effective bandwidth of the route expressed as
a number from 0 to 255 (255 is 100 percent loading).
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Command or Action
Purpose
• mtu—Minimum maximum transmission unit (MTU) size
of the route in bytes in the range 0 to 4294967295.
Step 19
set metric-type {type-1 | type-2}
Sets the OSPF external metric type for redistributed routes.
Example:
Switch(config-route-map)# set metric-type
type-2
Step 20
set metric-type internal
Example:
Sets the multi-exit discriminator (MED) value on prefixes
advertised to external BGP neighbor to match the IGP metric
of the next hop.
Switch(config-route-map)# set metric-type
internal
Step 21
set weight number
Sets the BGP weight for the routing table. The value can be
from 1 to 65535.
Example:
Switch(config-route-map)# set weight 100
Step 22
Returns to privileged EXEC mode.
end
Example:
Switch(config-route-map)# end
Step 23
show route-map
Displays all route maps configured or only the one specified to
verify configuration.
Example:
Switch# show route-map
Step 24
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
How to Control Route Distribution
Although each of Steps 3 through 14 in the following section is optional, you must enter at least one match
route-map configuration command and one set route-map configuration command.
Note
The keywords are the same as defined in the procedure to configure the route map for redistritbution.
The metrics of one routing protocol do not necessarily translate into the metrics of another. For example, the
RIP metric is a hop count, and the IGRP metric is a combination of five qualities. In these situations, an
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artificial metric is assigned to the redistributed route. Uncontrolled exchanging of routing information between
different routing protocols can create routing loops and seriously degrade network operation.
If you have not defined a default redistribution metric that replaces metric conversion, some automatic metric
translations occur between routing protocols:
• RIP can automatically redistribute static routes. It assigns static routes a metric of 1 (directly connected).
• Any protocol can redistribute other routing protocols if a default mode is in effect.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
router { rip | ospf | eigrp}
Enters router configuration mode.
Example:
Switch(config)# router eigrp 10
Step 3
redistribute protocol [process-id] {level-1 | level-1-2 |
level-2} [metric metric-value] [metric-type type-value]
[match internal | external type-value] [tag tag-value]
[route-map map-tag] [weight weight] [subnets]
Redistributes routes from one routing protocol to another
routing protocol. If no route-maps are specified, all routes
are redistributed. If the keyword route-map is specified
with no map-tag, no routes are distributed.
Example:
Switch(config-router)# redistribute eigrp 1
Step 4
default-metric number
Cause the current routing protocol to use the same metric
value for all redistributed routes ( RIP and OSPF).
Example:
Switch(config-router)# default-metric 1024
Step 5
default-metric bandwidth delay reliability loading mtu
Cause the EIGRP routing protocol to use the same metric
value for all non-EIGRP redistributed routes.
Example:
Switch(config-router)# default-metric 1000 100
250 100 1500
Step 6
Returns to privileged EXEC mode.
end
Example:
Switch(config-router)# end
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Policy-Based Routing
Step 7
Command or Action
Purpose
show route-map
Displays all route maps configured or only the one
specified to verify configuration.
Example:
Switch# show route-map
Step 8
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Related Topics
Information About Policy-Based Routing, on page 152
Other OSPF Parameters, on page 51
Policy-Based Routing
Information About Policy-Based Routing
You can use policy-based routing (PBR) to configure a defined policy for traffic flows. By using PBR, you
can have more control over routing by reducing the reliance on routes derived from routing protocols. PBR
can specify and implement routing policies that allow or deny paths based on:
• Identity of a particular end system
• Application
• Protocol
You can use PBR to provide equal-access and source-sensitive routing, routing based on interactive versus
batch traffic, or routing based on dedicated links. For example, you could transfer stock records to a corporate
office on a high-bandwidth, high-cost link for a short time while transmitting routine application data such
as e-mail over a low-bandwidth, low-cost link.
With PBR, you classify traffic using access control lists (ACLs) and then make traffic go through a different
path. PBR is applied to incoming packets. All packets received on an interface with PBR enabled are passed
through route maps. Based on the criteria defined in the route maps, packets are forwarded (routed) to the
appropriate next hop.
• Route map statement marked as permit is processed as follows:
◦A match command can match on length or multiple ACLs. A route map statement can contain
multiple match commands. Logical or algorithm function is performed across all the match
commands to reach a permit or deny decision.
For example:
match length A B
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match ip address acl1 acl2
match ip address acl3
A packet is permitted if it is permitted by match length A B or acl1 or acl2 or acl3
◦If the decision reached is permit, then the action specified by the set command is applied on the
packet .
◦If the decision reached is deny, then the PBR action (specified in the set command) is not applied.
Instead the processing logic moves forward to look at the next route-map statement in the sequence
(the statement with the next higher sequence number). If no next statement exists, PBR processing
terminates, and the packet is routed using the default IP routing table.
• For PBR, route-map statements marked as deny are not supported.
You can use standard IP ACLs to specify match criteria for a source address or extended IP ACLs to specify
match criteria based on an application, a protocol type, or an end station. The process proceeds through the
route map until a match is found. If no match is found, normal destination-based routing occurs. There is an
implicit deny at the end of the list of match statements.
If match clauses are satisfied, you can use a set clause to specify the IP addresses identifying the next hop
router in the path.
For details about PBR commands and keywords, see Cisco IOS IP Command Reference, Volume 2 of 3:
Routing Protocols.
Related Topics
Information About Route Maps, on page 146
How to Configure a Route Map
How to Control Route Distribution, on page 150
Policy-Based Routing Using Object Tracking
You can configure policy-based routing (PBR) to use object tracking to verify the most viable next-hop IP
address to which to forward packets, using an Internet Control Message Protocol (ICMP) ping as the verification
method.
PBR with Object Tracking is most suitable for devices that have multiple Ethernet connections as the next
hop. Normally, Ethernet interfaces connect to DSL modems or cable modems, and do not detect a failure
upstream, in the ISP broadband network. The Ethernet interface remains up, and any form of static routing
points to that interface. PBR with object tracking allows you to back up two Ethernet interfaces, determine
the interface that is available by sending ICMP pings to verify reachability, and then route traffic to that
interface.
To verify the next-hop IP address for the device, PBR informs the object-tracking process that it is interested
in tracking a certain object. The tracking process, in turn, informs PBR when the state of the object changes.
Note
VRF is not supported with PBR using Object Tracking.
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How to Configure PBR
• To use PBR, you must have the IP Services feature set enabled on the switch or stack master.
• Multicast traffic is not policy-routed. PBR applies to only to unicast traffic.
• You can enable PBR on a routed port or an SVI.
• The switch does not support route-map deny statements for PBR.
• The switch supports PBR based on match length.
• You can apply a policy route map to an EtherChannel port channel in Layer 3 mode, but you cannot
apply a policy route map to a physical interface that is a member of the EtherChannel. If you try to do
so, the command is rejected. When a policy route map is applied to a physical interface, that interface
cannot become a member of an EtherChannel.
• You can define a maximum of 128 IP policy route maps on the switch or switch stack.
• You can define a maximum of 512 access control entries (ACEs) for PBR on the switch or switch stack.
• When configuring match criteria in a route map, follow these guidelines:
◦Do not match ACLs that permit packets destined for a local address. PBR would forward these
packets, which could cause ping or Telnet failure or route protocol flappping.
◦Do not match ACLs with deny ACEs. Packets that match a deny ACE are sent to the CPU, which
could cause high CPU utilization.
• VRF and PBR are mutually exclusive on a switch interface. You cannot enable VRF when PBR is
enabled on an interface. The reverse is also true, you cannot enable PBR when VRF is enabled on an
interface.
• Web Cache Communication Protocol (WCCP) and PBR are mutually exclusive on a switch interface.
You cannot enable WCCP when PBR is enabled on an interface. The reverse is also true, you cannot
enable PBR when WCCP is enabled on an interface.
• The number of hardware entries used by PBR depends on the route map itself, the ACLs used, and the
order of the ACLs and route-map entries.
• PBR based on TOS, DSCP and IP Precedence are not supported.
• Set interface, set default next-hop and set default interface are not supported.
• ip next-hop recursive and ip next-hop verify availability features are not available and the next-hop
should be directly connected.
• Policy-maps with no set actions are supported. Matching packets are routed normally.
• Policy-maps with no match clauses are supported. Set actions are applied to all packets.
By default, PBR is disabled on the switch. To enable PBR, you must create a route map that specifies the
match criteria and the resulting action. Then, you must enable PBR for that route map on an interface. All
packets arriving on the specified interface matching the match clauses are subject to PBR.
Packets that are generated by the switch, or local packets, are not normally policy-routed. When you globally
enable local PBR on the switch, all packets that originate on the switch are subject to local PBR. Local PBR
is disabled by default.
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Policy-Based Routing
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
route-map map-tag [permit] [sequence number] Defines route maps that are used to control where packets are output,
and enters route-map configuration mode.
Example:
Switch(config)# route-map pbr-map permit
• map-tag — A meaningful name for the route map. The ip
policy route-map interface configuration command uses this
name to reference the route map. Multiple route-map statements
with the same map tag define a single route map.
• (Optional) permit — If permit is specified and the match
criteria are met for this route map, the route is policy routed
as defined by the set actions.
• (Optional) sequence number — The sequence number shows
the position of the route-map statement in the given route map.
Step 3
match ip address {access-list-number |
access-list-name} [access-list-number
|...access-list-name]
Matches the source and destination IP addresses that are permitted
by one or more standard or extended access lists. ACLs can match
on more than one source and destination IP address.
Example:
If you do not specify a match command, the route map is applicable
to all packets.
Switch(config-route-map)# match ip
address 110 140
Step 4
Matches the length of the packet.
match length min max
Example:
Switch(config-route-map)# match length
64 1500
Step 5
set ip next-hop ip-address [...ip-address]
Example:
Specifies the action to be taken on the packets that match the criteria.
Sets next hop to which to route the packet (the next hop must be
adjacent).
Switch(config-route-map)# set ip next-hop
10.1.6.2
Step 6
set ip next-hop verify-availability
[next-hop-address sequence track object]
Configures the route map to verify the reachability of the tracked
object.
Note
Example:
This command is not supported on IPv6 and
VRF.
Switch(config-route-map)# set ip next-hop
verify-availability 95.1.1.2.1 track 100
Step 7
Returns to global configuration mode.
exit
Example:
Switch(config-route-map)# exit
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Policy-Based Routing
Step 8
Command or Action
Purpose
interface interface-id
Enters interface configuration mode, and specifies the interface to
be configured.
Example:
Switch(config)# interface gigabitethernet
1/0/1
Step 9
ip policy route-map map-tag
Example:
Switch(config-if)# ip policy route-map
pbr-map
Step 10
ip route-cache policy
Enables PBR on a Layer 3 interface, and identify the route map to
use. You can configure only one route map on an interface. However,
you can have multiple route map entries with different sequence
numbers. These entries are evaluated in the order of sequence number
until the first match. If there is no match, packets are routed as usual.
(Optional) Enables fast-switching PBR. You must enable PBR before
enabling fast-switching PBR.
Example:
Switch(config-if)# ip route-cache policy
Step 11
exit
Returns to global configuration mode.
Example:
Switch(config-if)# exit
Step 12
ip local policy route-map map-tag
Example:
(Optional) Enables local PBR to perform policy-based routing on
packets originating at the switch. This applies to packets generated
by the switch, and not to incoming packets.
Switch(config)# ip local policy route-map
local-pbr
Step 13
end
Returns to privileged EXEC mode.
Example:
Switch(config)# end
Step 14
show route-map [map-name]
(Optional) Displays all the route maps configured or only the one
specified to verify configuration.
Example:
Switch# show route-map
Step 15
show ip policy
(Optional) Displays policy route maps attached to the interface.
Example:
Switch# show ip policy
Step 16
show ip local policy
(Optional) Displays whether or not local policy routing is enabled
and, if so, the route map being used.
Example:
Switch# show ip local policy
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Filtering Routing Information
Filtering Routing Information
You can filter routing protocol information by performing the tasks described in this section.
Note
When routes are redistributed between OSPF processes, no OSPF metrics are preserved.
Setting Passive Interfaces
To prevent other routers on a local network from dynamically learning about routes, you can use the
passive-interface router configuration command to keep routing update messages from being sent through
a router interface. When you use this command in the OSPF protocol, the interface address you specify as
passive appears as a stub network in the OSPF domain. OSPF routing information is neither sent nor received
through the specified router interface.
In networks with many interfaces, to avoid having to manually set them as passive, you can set all interfaces
to be passive by default by using the passive-interface default router configuration command and manually
setting interfaces where adjacencies are desired.
Use a network monitoring privileged EXEC command such as show ip ospf interface to verify the interfaces
that you enabled as passive, or use the show ip interface privileged EXEC command to verify the interfaces
that you enabled as active.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
router { rip | ospf | eigrp}
Enters router configuration mode.
Example:
Switch(config)# router ospf
Step 3
passive-interface interface-id
Suppresses sending routing updates through the
specified Layer 3 interface.
Example:
Switch(config-router)# passive-interface
gigabitethernet 1/0/1
Step 4
passive-interface default
(Optional) Sets all interfaces as passive by default.
Example:
Switch(config-router)# passive-interface default
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Filtering Routing Information
Step 5
Command or Action
Purpose
no passive-interface interface type
(Optional) Activates only those interfaces that need
to have adjacencies sent.
Example:
Switch(config-router)# no passive-interface
gigabitethernet1/0/3 gigabitethernet 1/0/5
Step 6
network network-address
(Optional) Specifies the list of networks for the routing
process. The network-address is an IP address.
Example:
Switch(config-router)# network 10.1.1.1
Step 7
Returns to privileged EXEC mode.
end
Example:
Switch(config-router)# end
Step 8
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Controlling Advertising and Processing in Routing Updates
You can use the distribute-list router configuration command with access control lists to suppress routes
from being advertised in routing updates and to prevent other routers from learning one or more routes. When
used in OSPF, this feature applies to only external routes, and you cannot specify an interface name.
You can also use a distribute-list router configuration command to avoid processing certain routes listed in
incoming updates. (This feature does not apply to OSPF.)
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
router { rip | eigrp}
Enters router configuration mode.
Example:
Switch(config)# router eigrp 10
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Filtering Routing Information
Command or Action
Step 3
Purpose
Permits or denies routes from being advertised in
distribute-list {access-list-number | access-list-name} out
[interface-name | routing process | autonomous-system-number] routing updates, depending upon the action listed
in the access list.
Example:
Switch(config-router)# distribute 120 out
gigabitethernet 1/0/7
Step 4
distribute-list {access-list-number | access-list-name} in
[type-number]
Suppresses processing in routes listed in updates.
Example:
Switch(config-router)# distribute-list 125 in
Step 5
Returns to privileged EXEC mode.
end
Example:
Switch(config-router)# end
Step 6
(Optional) Saves your entries in the configuration
file.
copy running-config startup-config
Example:
Switch# copy running-config startup-config
Filtering Sources of Routing Information
Because some routing information might be more accurate than others, you can use filtering to prioritize
information coming from different sources. An administrative distance is a rating of the trustworthiness of a
routing information source, such as a router or group of routers. In a large network, some routing protocols
can be more reliable than others. By specifying administrative distance values, you enable the router to
intelligently discriminate between sources of routing information. The router always picks the route whose
routing protocol has the lowest administrative distance.
Because each network has its own requirements, there are no general guidelines for assigning administrative
distances.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
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Configuring IP Unicast Routing
Managing Authentication Keys
Step 2
Command or Action
Purpose
router { rip | ospf | eigrp}
Enters router configuration mode.
Example:
Switch(config)# router eigrp 10
Step 3
distance weight {ip-address {ip-address mask}} Defines an administrative distance.
[ip access list]
weight—The administrative distance as an integer from 10 to
255. Used alone, weight specifies a default administrative distance
Example:
that is used when no other specification exists for a routing
Switch(config-router)# distance 50 10.1.5.1 information source. Routes with a distance of 255 are not installed
in the routing table.
(Optional) ip access list—An IP standard or extended access list
to be applied to incoming routing updates.
Step 4
Returns to privileged EXEC mode.
end
Example:
Switch(config-router)# end
Step 5
show ip protocols
Displays the default administrative distance for a specified routing
process.
Example:
Switch# show ip protocols
Step 6
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Managing Authentication Keys
Key management is a method of controlling authentication keys used by routing protocols. Not all protocols
can use key management. Authentication keys are available for EIGRP and RIP Version 2.
Prerequisites
Before you manage authentication keys, you must enable authentication. See the appropriate protocol section
to see how to enable authentication for that protocol. To manage authentication keys, define a key chain,
identify the keys that belong to the key chain, and specify how long each key is valid. Each key has its own
key identifier (specified with the key number key chain configuration command), which is stored locally. The
combination of the key identifier and the interface associated with the message uniquely identifies the
authentication algorithm and Message Digest 5 (MD5) authentication key in use.
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Configuring IP Unicast Routing
Managing Authentication Keys
How to Configure Authentication Keys
You can configure multiple keys with life times. Only one authentication packet is sent, regardless of how
many valid keys exist. The software examines the key numbers in order from lowest to highest, and uses the
first valid key it encounters. The lifetimes allow for overlap during key changes. Note that the router must
know these lifetimes.
DETAILED STEPS
Step 1
Command or Action
Purpose
configure terminal
Enters global configuration mode.
Example:
Switch# configure terminal
Step 2
key chain name-of-chain
Identifies a key chain, and enter key chain configuration mode.
Example:
Switch(config)# key chain key10
Step 3
key number
Identifies the key number. The range is 0 to 2147483647.
Example:
Switch(config-keychain)# key 2000
Step 4
key-string text
Identifies the key string. The string can contain from 1 to 80
uppercase and lowercase alphanumeric characters, but the first
character cannot be a number.
Example:
Switch(config-keychain)# Room 20, 10th
floor
Step 5
accept-lifetime start-time {infinite | end-time |
duration seconds}
Switch(config-keychain)# accept-lifetime
12:30:00 Jan 25 1009 infinite
The start-time and end-time syntax can be either hh:mm:ss Month
date year or hh:mm:ss date Month year. The default is forever
with the default start-time and the earliest acceptable date as
January 1, 1993. The default end-time and duration is infinite.
send-lifetime start-time {infinite | end-time |
duration seconds}
(Optional) Specifies the time period during which the key can be
sent.
Example:
Step 6
(Optional) Specifies the time period during which the key can be
received.
Example:
Switch(config-keychain)# accept-lifetime
23:30:00 Jan 25 1019 infinite
The start-time and end-time syntax can be either hh:mm:ss Month
date year or hh:mm:ss date Month year. The default is forever
with the default start-time and the earliest acceptable date as
January 1, 1993. The default end-time and duration is infinite.
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Monitoring and Maintaining the IP Network
Step 7
Command or Action
Purpose
end
Returns to privileged EXEC mode.
Example:
Switch(config-keychain)# end
Step 8
show key chain
Displays authentication key information.
Example:
Switch# show key chain
Step 9
copy running-config startup-config
(Optional) Saves your entries in the configuration file.
Example:
Switch# copy running-config startup-config
Monitoring and Maintaining the IP Network
You can remove all contents of a particular cache, table, or database. You can also display specific statistics.
Table 17: Commands to Clear IP Routes or Display Route Status
clear ip route {network [mask | *]}
Clears one or more routes from the IP routing table.
show ip protocols
Displays the parameters and state of the active routing
protocol process.
show ip route [address [mask]
[longer-prefixes]] | [protocol [process-id]]
Displays the current state of the routing table.
show ip route summary
Displays the current state of the routing table in summary
form.
show ip route supernets-only
Displays supernets.
show ip cache
Displays the routing table used to switch IP traffic.
show route-map [map-name]
Displays all route maps configured or only the one specified.
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Configuring IP Unicast Routing
Additional References for Configuring IP Unicast Routing
Additional References for Configuring IP Unicast Routing
Related Documents
Related Topic
Document Title
Command reference
Command Reference, Cisco IOS
Release 15.2(2)E (Catalyst 3750-X
and 3560-X Switches)
Error Message Decoder
Description
Link
To help you research and resolve system error
messages in this release, use the Error Message
Decoder tool.
https://www.cisco.com/cgi-bin/Support/Errordecoder/
index.cgi
Standards and RFCs
Standard/RFC
Title
None
—
MIBs
MIB
MIBs Link
All supported MIBs for this release.
To locate and download MIBs for selected platforms,
Cisco IOS releases, and feature sets, use Cisco MIB
Locator found at the following URL:
http://www.cisco.com/go/mibs
Software Configuration Guide, Cisco IOS Release 15.2(2)E (Catalyst 3750-X and 3560-X Switches)
163
Configuring IP Unicast Routing
Additional References for Configuring IP Unicast Routing
Technical Assistance
Description
Link
The Cisco Support website provides extensive online http://www.cisco.com/support
resources, including documentation and tools for
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