Configuring Interface Characteristics

Configuring Interface Characteristics
CH A P T E R
10
Configuring Interfaces
This chapter defines the types of interfaces on the Cisco ME 3800X and ME 3600X switches and
describes how to configure them.
Note
•
Understanding Interface Types, page 10-1
•
Using Interface Configuration Mode, page 10-6
•
Using the Ethernet Management Port, page 10-10
•
Configuring Ethernet Interfaces, page 10-13
•
Configuring Layer 3 Interfaces, page 10-19
•
Configuring the Interface MTU, page 10-20
•
Monitoring and Maintaining the Interfaces, page 10-21
For complete syntax and usage information for the commands used in this chapter, see the switch
command reference for this release and the online Cisco IOS Interface Command Reference,
Release 12.2.
Understanding Interface Types
This section describes the different types of interfaces supported by the switch with references to
chapters that contain more detailed information about configuring these interface types. The rest of the
chapter describes configuration procedures for physical interface characteristics.
•
NNI Port Type, page 10-2
•
Port-Based VLANs, page 10-2
•
Switch Ports, page 10-2
•
Routed Ports, page 10-3
•
Ethernet Management Port, page 10-4
•
Switch Virtual Interfaces, page 10-4
•
EtherChannel Port Groups, page 10-4
•
Connecting Interfaces, page 10-5
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NNI Port Type
All Cisco ME 3800X and 3600X ports are network node interfaces (NNIs), which are typically
connected to a router or to another switch. The default status for an NNI is administratively up to allow
a service provider remote access to the switch during initial configuration.
Port-Based VLANs
A VLAN is a switched network that is logically segmented by function, team, or application, without
regard to the physical location of the users. For more information about VLANs, see Chapter 11,
“Configuring VLANs.” Packets received on a port are forwarded only to ports that belong to the same
VLAN as the receiving port. Network devices in different VLANs cannot communicate with one another
without a Layer 3 device to route traffic between the VLANs.
VLAN partitions provide hard firewalls for traffic in the VLAN, and each VLAN has its own MAC
address table. A VLAN comes into existence when a local port is associated with the VLAN ID or when
a user creates te VLAN ID.
To configure VLANs, use the vlan vlan-id global configuration command to enter VLAN configuration
mode. The VLAN configurations for VLAN IDs 1 to 1005 are saved in the VLAN database.
Extended-range VLANs (VLAN IDs 1006 to 4094) are not added to the VLAN database. VLAN
configuration is saved in the switch running configuration, and you can save it in the switch startup
configuration file by entering the copy running-config startup-config privileged EXEC command.
Add ports to a VLAN by using the switchport interface configuration commands:
•
Identify the interface.
•
For a trunk port, set trunk characteristics, and if desired, define the VLANs to which it can belong.
•
For an access port, set and define the VLAN to which it belongs.
To isolate VLANs of different customers in a service-provider network, Cisco ME switches use UNI
VLANs. Local switching does not occur among user network interfaces (UNIs) and enhanced network
interfaces (ENIs) on the switch that belong to the same UNI isolated VLAN. Local switching is allowed
among ports that belong to a UNI community VLAN. Because all ports on the ME 3800X and 3600X
switches are NNIs, UNI VLAN configuration has no effect. Local switching is allowed between NNIs.
Switch Ports
Switch ports are Layer 2 only interfaces associated with a physical port. Switch ports belong to one or
more VLANs. You can configure a port as an access port or trunk port. Switch ports are used for
managing the physical interface and associated Layer 2 protocols and do not handle routing or bridging.
Configure switch ports by using the switchport interface configuration commands. Use the switchport
command with no keywords to put an interface that is in Layer 3 mode into Layer 2 mode.
Note
When you put an interface that is in Layer 3 mode into Layer 2 mode, the previous configuration
information related to the affected interface might be lost, and the interface is returned to its default
configuration.
For detailed information about configuring access port and trunk port characteristics, see Chapter 11,
“Configuring VLANs.”
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Access Ports
An access port belongs to and carries the traffic of only one VLAN. Traffic is received and sent in native
formats with no VLAN tagging. Traffic arriving on an access port is assumed to belong to the VLAN
assigned to the port. If an access port receives an IEEE 802.1Q tagged packet, the packet is dropped, and
the source address is not learned. IEEE 802.1x can also be used for VLAN assignment.
You manually assign static access ports to a VLAN.
Trunk Ports
An IEEE 802.1Q trunk port carries the traffic of multiple VLANs and by default is a member of all
VLANs in the VLAN database. A trunk port supports simultaneous tagged and untagged traffic. An
IEEE 802.1Q trunk port is assigned a default Port VLAN ID (PVID), and all untagged traffic travels on
the port default PVID. All untagged traffic and tagged traffic with a NULL VLAN ID are assumed to
belong to the port default PVID. A packet with a VLAN ID equal to the outgoing port default PVID is
sent untagged. All other traffic is sent with a VLAN tag.
Although by default a trunk port is a member of multiple VLANs, you can limit VLAN membership by
configuring an allowed list of VLANs for each trunk port. The list of allowed VLANs does not affect
any other port but the associated trunk port. By default, all possible VLANs (VLAN ID 1 to 4094) are
in the allowed list. A trunk port can become a member of a VLAN only if the VLAN is in the enabled
state.
For more information about trunk ports, see Chapter 11, “Configuring VLANs.”
Routed Ports
A routed port is a physical port that acts like a port on a router; it does not have to be connected to a
router. A routed port is not associated with a particular VLAN, as is an access port. A routed port behaves
like a regular router interface, except that it does not support VLAN subinterfaces. Routed ports can be
configured with a Layer 3 routing protocol. A routed port is a Layer 3 interface only and does not support
Layer 2 protocols, such as STP.
Configure routed ports by putting the interface into Layer 3 mode with the no switchport interface
configuration command. Then assign an IP address to the port, enable routing, and assign routing
protocol characteristics by using the ip routing and router protocol global configuration commands.
Note
Entering a no switchport interface configuration command shuts down the interface and then re-enables
it, which might generate messages on the device to which the interface is connected. When you put an
interface that is in Layer 2 mode into Layer 3 mode, the previous configuration information related to
the affected interface might be lost.
The number of routed ports that you can configure is not limited by software. However, the
interrelationship between this number and the number of other features being configured might impact
CPU performance because of hardware limitations. See the “Configuring Layer 3 Interfaces” section on
page 10-19 for information about what happens when hardware resource limitations are reached.
For more information about IP unicast and multicast routing and routing protocols, see Chapter 29,
“Configuring IP Unicast Routing” and Chapter 35, “Configuring IP Multicast Routing.”
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Ethernet Management Port
The Ethernet management port, also referred to as the Gi0 or gigabitethernet0 port, is a Layer 3 host
port to which you can connect a PC. You can use the Ethernet management port instead of the switch
console port for network management.
See the “Using the Ethernet Management Port” section on page 10-10 for more information.
Switch Virtual Interfaces
A switch virtual interface (SVI) represents a VLAN of switch ports as one interface to the routing or
bridging function in the system. Only one SVI can be associated with a VLAN, but you need to configure
an SVI for a VLAN only when you wish to route between VLANs or to provide IP host connectivity to
the switch. By default, an SVI is created for the default VLAN (VLAN 1) to permit remote switch
administration. Additional SVIs must be explicitly configured.
Note
You cannot delete interface VLAN 1.
SVIs provide IP host connectivity only to the system; in Layer 3 mode, you can configure routing across
SVIs.
Although the switch supports a total of 1005 VLANs (and SVIs), the interrelationship between the
number of SVIs and routed ports and the number of other features being configured might impact CPU
performance because of hardware limitations. See the “Configuring Layer 3 Interfaces” section on
page 10-19 for information about what happens when hardware resource limitations are reached.
SVIs are created the first time that you enter the vlan interface configuration command for a VLAN
interface. The VLAN corresponds to the VLAN tag associated with data frames on an IEEE 802.1Q
encapsulated trunk or the VLAN ID configured for an access port. Configure a VLAN interface for each
VLAN for which you want to route traffic, and assign it an IP address. For more information, see the
“Manually Assigning IP Information” section on page 3-15.
Note
When you create an SVI, it does not become active until it is associated with a physical port.
SVIs support routing protocols. For more information about configuring IP routing, see Chapter 29,
“Configuring IP Unicast Routing,” and Chapter 35, “Configuring IP Multicast Routing.”
EtherChannel Port Groups
EtherChannel port groups treat multiple switch ports as one switch port. These port groups act as a single
logical port for high-bandwidth connections between switches or between switches and servers. An
EtherChannel balances the traffic load across the links in the channel. If a link within the EtherChannel
fails, traffic previously carried over the failed link changes to the remaining links. You can group
multiple trunk ports into one logical trunk port, group multiple access ports into one logical access port,
or group multiple routed ports into one logical routed port. Most protocols operate over either single
ports or aggregated switch ports and do not recognize the physical ports within the port group.
Exceptions are the Cisco Discovery Protocol (CDP), Link Aggregation Control Protocol (LACP), and
the Port Aggregation Protocol (PAgP), which operate only on physical NNI or ENI ports.
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When you configure an EtherChannel, you create a port-channel logical interface and assign an interface
to the EtherChannel. For Layer 3 interfaces, you manually create the logical interface by using the
interface port-channel global configuration command. Then you manually assign an interface to the
EtherChannel by using the channel-group interface configuration command. For Layer 2 interfaces, use
the channel-group interface configuration command to dynamically create the port-channel logical
interface. This command binds the physical and logical ports together. For more information, see
Chapter 28, “Configuring EtherChannels.”
Ethernet Flow Points
An Ethernet Flow Point (EFP) is a logical interface that connects an Ethernet Virtual Connection (EVC)
bridge domain to a physical port in a switch. Configuring a service instance on an interface creates a
pseudoport or EFP on which you configure EVC features.
You can configure EFP service instances only on Layer 2 ports. You can configure an EtherChannel with
a service instance, but you cannot add an interface to a channel group if it has a service instance
configured on it. EFPs do not support routing. EFPs do not support switchport commands.
Switch interfaces configured with service instances support a different range of features than interfaces
that do not have service instances. For more information on EVCs, see Chapter 12, “Configuring
Ethernet Virtual Connections (EVCs).”
Connecting Interfaces
Devices within a single VLAN can communicate directly through any switch. Ports in different VLANs
cannot exchange data without going through a routing device. With a standard Layer 2 switch, ports in
different VLANs have to exchange information through a router. By using the switch with routing
enabled, when you configure both VLAN 20 and VLAN 30 with an SVI to which an IP address is
assigned, packets can be sent from Host A to Host B directly through the switch with no need for an
external router (Figure 10-1).
Figure 10-1
Connecting VLANs with the Switch
Layer 3 switch
with routing enabled
SVI 1
Host A
SVI 2
172.20.129.1
Host B
VLAN 20
VLAN 30
101350
172.20.128.1
You can enable routing on all SVIs and routed ports on the switch. Whenever possible, to maintain high
performance, forwarding is done by the switch hardware. However, only IP Version 4 packets with
Ethernet II encapsulation can be routed in hardware. The switch routes only IP traffic. When IP routing
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protocol parameters and address configuration are added to an SVI or routed port, any IP traffic received
from these ports is routed. For more information, see Chapter 29, “Configuring IP Unicast Routing” and
Chapter 35, “Configuring IP Multicast Routing.”
Using Interface Configuration Mode
The switch supports these interface types:
Note
•
Physical ports—switch ports, routed ports
•
SVIs—switch virtual interfaces
•
Port-channels—EtherChannel interfaces
The switch also supports EFP service instances configured on physical interfaces. You configure EFPs
in service-instance configuration mode. See Chapter 12, “Configuring Ethernet Virtual Connections
(EVCs).”
You can also configure a range of interfaces (see the “Configuring a Range of Interfaces” section on
page 10-7).
To configure a physical interface (port), specify the interface type, the module number, and the switch port
number, and enter interface configuration mode.
•
Type—Gigabit Ethernet (gigabitethernet or gi) for 10/100/1000 Mb/s Ethernet ports, or small
form-factor pluggable (SFP) module Gigabit Ethernet interfaces.
•
Module number—The module or slot number on the switch (always 0 on the Cisco ME switch).
•
Port number—The interface number on the switch. The port numbers always begin at 1, starting with
the leftmost port when facing the front of the switch, for example, gigabitethernet 0/1. If there is
more than one interface type (for example, 10/100/1000 ports and SFP module ports), the port
numbers restart with the second interface type: gigabitethernet 0/1.
You can identify physical interfaces by physically checking the interface location on the switch. You can
also use the show privileged EXEC commands to display information about a specific interface or all
the interfaces on the switch. The remainder of this chapter primarily provides physical interface
configuration procedures.
Procedures for Configuring Interfaces
These general instructions apply to all interface configuration processes.
Step 1
Enter the configure terminal command at the privileged EXEC prompt:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#
Step 2
Enter the interface global configuration command. Identify the interface type and the number of the
connector. In this example, Fast Ethernet port 1 is selected:
Switch(config)# interface gigabitethernet0/1
Switch(config-if)#
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You do not need to add a space between the interface type and interface number. For example,
in the preceding line, you can specify either gigabitethernet 0/1, gigabitethernet0/1, gi 0/1, or
gi0/1.
Note
Step 3
Follow each interface command with the interface configuration commands that the interface requires.
The commands that you enter define the protocols and applications that will run on the interface. The
commands are collected and applied to the interface when you enter another interface command or enter
end to return to privileged EXEC mode.
You can also configure a range of interfaces by using the interface range or interface range macro
global configuration commands. Interfaces configured in a range must be the same type and must be
configured with the same feature options.
Step 4
After you configure an interface, verify its status by using the show privileged EXEC commands listed
in the “Monitoring and Maintaining the Interfaces” section on page 10-21.
Enter the show interfaces privileged EXEC command to see a list of all interfaces on or configured for
the switch. A report is provided for each interface that the device supports or for the specified interface.
Configuring a Range of Interfaces
You can use the interface range global configuration command to configure multiple interfaces with the
same configuration parameters. When you enter the interface range configuration mode, all command
parameters that you enter are attributed to all interfaces within that range until you exit this mode.
Beginning in privileged EXEC mode, follow these steps to configure a range of interfaces with the
same parameters:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface range {port-range}
Specify the range of interfaces (VLANs or physical ports) to be
configured, and enter interface range configuration mode.
Step 3
•
You can use the interface range command to configure up to five
port ranges or a previously defined macro.
•
In a comma-separated port-range, you must enter the interface
type for each entry and enter spaces before and after the comma.
•
In a hyphen-separated port-range, you do not need to re-enter the
interface type, but you must enter a space before the hyphen.
You can now use the normal configuration commands to apply the
configuration parameters to all interfaces in the range.
Step 4
end
Return to privileged EXEC mode.
Step 5
show interfaces [interface-id]
Verify the configuration of the interfaces in the range.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.
When using the interface range global configuration command, note these guidelines:
•
Valid entries for port-range:
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– vlan vlan-ID - vlan-ID, where the VLAN ID is 1 to 4094
– gigabitethernet module/{first port} - {last port}, where the module is always 0
– tengigabitethernet module/{first port} - {last port}, where the module is always 0
– port-channel port-channel-number - port-channel-number, where the port-channel-number
is 1 to 26
Note
When you use the interface range command with port channels, the first and last port
channel number must be active port channels.
•
The interface range command only works with VLAN interfaces that have been configured with
the interface vlan command. The show running-config privileged EXEC command displays the
configured VLAN interfaces. VLAN interfaces not displayed by the show running-config
command cannot be used with the interface range command.
•
All interfaces defined as in a range must be the same type (all Fast Ethernet ports, all Gigabit
Ethernet ports, all EtherChannel ports, or all VLANs), but you can enter multiple ranges in a
command.
This example shows how to use the interface range global configuration command to set the speed on
ports 1 and 2 to 100 Mb/s:
Switch# configure terminal
Switch(config)# interface range gigabitethernet0/1 - 2
Switch(config-if-range)# speed 100
This example shows how to use a comma to add different interface type strings to the range to enable
Fast Ethernet ports 1 to 3 and Gigabit Ethernet ports 1 and 2 to receive IEEE 802.3x flow control pause
frames:
Switch# configure terminal
Switch(config)# interface range gigabitethernet0/1 - 3 , gigabitethernet0/5 - 6
Switch(config-if-range)# flowcontrol receive on
If you enter multiple configuration commands while you are in interface range mode, each command is
executed as it is entered. The commands are not batched together and executed after you exit interface
range mode. If you exit interface range configuration mode while the commands are being executed,
some commands might not be executed on all interfaces in the range. Wait until the command prompt
reappears before exiting interface range configuration mode.
Configuring and Using Interface Range Macros
You can create an interface range macro to automatically select a range of interfaces for configuration.
Before you can use the macro keyword in the interface range macro global configuration command
string, you must use the define interface-range global configuration command to define the macro.
Beginning in privileged EXEC mode, follow these steps to define an interface range macro:
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Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
define interface-range macro_name
interface-range
Define the interface-range macro, and save it in NVRAM.
Step 3
interface range macro macro_name
•
The macro_name is a 32-character maximum character string.
•
A macro can contain up to five comma-separated interface ranges.
•
Each interface-range must consist of the same port type.
Select the interface range to be configured using the values saved in
the interface-range macro called macro_name.
You can now use the normal configuration commands to apply the
configuration to all interfaces in the defined macro.
Step 4
end
Return to privileged EXEC mode.
Step 5
show running-config | include define
Show the defined interface range macro configuration.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.
Use the no define interface-range macro_name global configuration command to delete a macro.
When using the define interface-range global configuration command, note these guidelines:
•
Valid entries for interface-range:
– vlan vlan-ID - vlan-ID, where the VLAN ID is 1 to 4094
– gigabitethernet module/{first port} - {last port}, where the module is always 0
– tengigabitethernet module/{first port} - {last port}, where the module is always 0
– port-channel port-channel-number - port-channel-number, where the port-channel-number
is 1 to 26.
Note
When you use the interface ranges with port channels, the first and last port channel number
must be active port channels.
•
You must add a space between the first interface number and the hyphen when entering an
interface-range. For example, gigabitethernet0/1 - 2 is a valid range; gigabitethernet0/1-2 is not
a valid range.
•
The VLAN interfaces must have been configured with the interface vlan command. The show
running-config privileged EXEC command displays the configured VLAN interfaces. VLAN
interfaces not displayed by the show running-config command cannot be used as interface-ranges.
•
All interfaces defined as in a range must be the same type (all Fast Ethernet ports, all Gigabit
Ethernet ports, all EtherChannel ports, or all VLANs), but you can combine multiple interface types
in a macro.
This example shows how to define an interface-range named enet_list to include ports 1 and 2 and to
verify the macro configuration:
Switch# configure terminal
Switch(config)# define interface-range enet_list gigabitethernet0/1 - 2
Switch(config)# end
Switch# show running-config | include define
define interface-range enet_list GigabitEthernet0/1 - 2
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This example shows how to create a multiple-interface macro named macro1 and assign all of the
interfaces in the range to a VLAN:
Switch# configure terminal
Switch(config)# define interface-range macro1 gigabitethernet0/1 - 2, gigabitethernet0/5 6
Switch(config)# interface range macro macro1
Switch(config-if-range)# switchport access vlan 20
Switch(config-if-range)# end
This example shows how to enter interface range configuration mode for the interface-range
macro enet_list:
Switch# configure terminal
Switch(config)# interface range macro enet_list
Switch(config-if-range)#
This example shows how to delete the interface-range macro enet_list and to verify that it was deleted.
Switch# configure terminal
Switch(config)# no define interface-range enet_list
Switch(config)# end
Switch# show run | include define
Switch#
Using the Ethernet Management Port
•
Understanding the Ethernet Management Port, page 10-10
•
Supported Features on the Ethernet Management Port, page 10-12
•
Configuring the Ethernet Management Port, page 10-12
•
TFTP and the Ethernet Management Port, page 10-12
Understanding the Ethernet Management Port
The Ethernet management port is port Gi0 or gigabitethernet0, a Layer 3 host port to which you can
connect a PC. You can use the Ethernet management port instead of the switch console port for network
management.
Note
You cannot configure an EFP service instance on the Ethernet management port.
When connecting a PC to the Ethernet management port, you must assign an IP address. Connect the
Ethernet management port to the PC as shown in Figure 10-2.
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Switch
Network
cloud
Connecting a Switch to a PC
Ethernet
management
port
PC
Network
ports
157549
Figure 10-2
By default, the Ethernet management port is enabled. The switch cannot route packets from the Ethernet
management port to a network port or receive routed packets from a network port.
Even though the Ethernet management port does not support routing, you might need to enable routing
protocols on the port. For example, in Figure 10-3, you must enable routing protocols on the Ethernet
management port when the PC is two or more hops away from the switch and the packets must pass
through two or more Layer 3 devices to reach the PC.
Figure 10-3
Switch
Network Example with Routing Protocols Enabled
Ethernet
management
port
PC
Network
cloud
Network
ports
157551
Network
cloud
In Figure 10-3, if the Ethernet management port and the network ports are associated with the same
routing process, the routes are propagated in this manner:
•
The routes from the Ethernet management port are propagated through the network ports to the
network.
•
The routes from the network ports are propagated through the Ethernet management port to the
network.
Because routing is not supported between the Ethernet management port and the network ports, traffic
cannot be sent or received between these ports. If traffic is sent or received, data packet loops occur
between the ports, which disrupts the switch and network operation. Configure route filters to avoid
routes between the Ethernet management port and the network ports and to prevent the loops.
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Supported Features on the Ethernet Management Port
The Ethernet management port supports these features:
Caution
•
Telnet with passwords
•
TFTP
•
Secure Shell (SSH)
•
DHCP-based autoconfiguration
•
SMNP (only the ENTITY-MIB and the IF-MIB)
•
IP ping
•
Interface features
•
Speed—1000 Mb/s, and autonegotiation
•
Duplex mode—Full, half, and autonegotiation
•
Loopback detection
•
Cisco Discovery Protocol (CDP)
•
DHCP relay agent
•
IPv4 access control lists (ACLs)
•
Routing protocols
Before enabling a feature on the Ethernet management port, make sure that the feature is supported. If
you try to configure an unsupported feature on the Ethernet Management port, the feature might not work
properly, and the switch might fail.
Configuring the Ethernet Management Port
To specify the Ethernet management port in the CLI, enter gigabitethernet0.
To disable the port, use the shutdown interface configuration command. To enable the port, use the no
shutdown interface configuration command.
You can monitor the Ethernet management port LED to determine the link status to the PC. The LED is
green (on) when the link is active, and the LED is off when the link is down. The LED is amber when
there is a POST failure.
To display the link status, use the show interfaces gigabitethernet 0 privileged EXEC command.
TFTP and the Ethernet Management Port
Use the commands in Table 1 when using TFTP to download or upload a configuration file to the boot
loader.
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Table 1
Boot Loader Commands
Command
Description
arp [ip_address]
Displays the currently cached ARP1 table when this command is entered
without the ip_address parameter.
Enables ARP to associate a MAC address with the specified IP address
when this command is entered with the ip_address parameter.
mgmt_clr
Clears the statistics for the Ethernet management port.
mgmt_init
Starts the Ethernet management port.
mgmt_show
Displays the statistics for the Ethernet management port.
ping host_ip_address
Sends ICMP ECHO_REQUEST packets to the specified network host.
boot tftp:/file-url ...
Loads and boots an executable image from the TFTP server and enters
the command-line interface.
For more details, see the command reference for this release.
copy tftp:/source-file-url
filesystem:/destination-fileurl
Copies a Cisco IOS image from the TFTP server to the specified
location.
For more details, see the command reference for this release.
1. ARP = Address Resolution Protocol.
Configuring Ethernet Interfaces
•
Default Ethernet Interface Configuration, page 10-13
•
Configuring Interface Speed and Duplex Mode, page 10-14
•
Configuring IEEE 802.3x Flow Control, page 10-16
•
Configuring Auto-MDIX on an Interface, page 10-17
•
Adding a Description for an Interface, page 10-18
Default Ethernet Interface Configuration
Table 10-2 shows the Ethernet interface default configuration. For more details on the VLAN parameters
listed in the table, see Chapter 11, “Configuring VLANs.” For details on controlling traffic to the port,
see Chapter 20, “Configuring Traffic Control.”
Note
To configure Layer 2 parameters, if the interface is in Layer 3 mode, you must enter the switchport
interface configuration command without any parameters to put the interface into Layer 2 mode. This
shuts down the interface and then re-enables it, which might generate messages on the device to which
the interface is connected. When you put an interface that is in Layer 3 mode into Layer 2 mode, the
previous configuration information related to the affected interface might be lost, and the interface is
returned to its default configuration.
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Table 10-2
Default Ethernet Configuration
Feature
Default Setting
Operating mode
Layer 2 or switching mode (switchport command).
Allowed VLAN range
VLANs 1– 4094.
Default VLAN (for access ports)
VLAN 1 (Layer 2 interfaces only).
Native VLAN (for IEEE 802.1Q trunks)
VLAN 1 (Layer 2 interfaces only).
VLAN trunking
Switchport mode access (Layer 2 interfaces only).
Port enable state
Enabled.
Port description
None defined.
Speed
Autonegotiate.
Duplex mode
Autonegotiate.
IEEE 802.3x flow control
Flow control is set to receive: off. It is always off for sent packets.
EtherChannel
Disabled on all Ethernet ports. See Chapter 28, “Configuring
EtherChannels.”
Broadcast, multicast, and unicast storm control
Disabled. See the “Default Storm Control Configuration” section on
page 20-3.
Port Fast
Disabled. See the “Default Optional Spanning-Tree Configuration”
section on page 16-5.
Auto-MDIX
Enabled.
Cisco Discovery Protocol (CDP)
Enabled.
Configuring Interface Speed and Duplex Mode
Ethernet interfaces on the switch operate at 10, 100, or 1000 Mb/s or and in either full- or half-duplex
mode. In full-duplex mode, two stations can send and receive traffic at the same time. Normally, 10-Mb/s
ports operate in half-duplex mode, which means that stations can either receive or send traffic.
Switch models include combinations Gigabit Ethernet (10/100/1000-Mb/s) ports and small form-factor
pluggable (SFP) module slots supporting SFP modules.
•
Speed and Duplex Configuration Guidelines, page 10-14
•
Setting the Interface Speed and Duplex Parameters, page 10-15
Speed and Duplex Configuration Guidelines
When configuring an interface speed and duplex mode, note these guidelines:
•
You can configure interface speed on Gigabit Ethernet (10/100/1000-Mb/s) ports. You can configure
Gigabit Ethernet ports to full-duplex mode or to autonegotiate. You also can configure Gigabit
Ethernet ports to half-duplex mode if the speed is 10 or 100 Mb/s. Half-duplex mode is not
supported on Gigabit Ethernet ports operating at 1000 Mb/s.
•
You cannot configure speed on SFP module ports or on 10 Gigabit Ethernet ports, but you can
configure speed to not negotiate (nonegotiate) on SFP module ports if connected to a device that
does not support autonegotiation.
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The exception is when a 1000BASE-T SFP module is in the SFP module slot, you can configure
speed as 10, 100, or 1000 Mb/s, or auto, but not as nonegotiate.
On a 100BASE-FX SFP module, you cannot configure the speed as nonegotiate.
•
You cannot configure duplex mode on 10 GigabitEthernet ports. The duplex command is not
available.
•
You cannot configure duplex mode on SFP module ports; they operate in full-duplex mode except
in these situations:
– When a Cisco1000BASE-T SFP module is in the SFP module slot, you can configure duplex
mode to auto or full. Half-duplex mode is supported with the auto setting.
– When a Cisco100BASE-FX SFP module is in the SFP module slot, you can configure duplex
mode to half or full. Although the auto keyword is available, it puts the interface in half-duplex
mode (the default for this SFP module) because the 100BASE-FX SFP module does not support
autonegotiation.
Caution
•
If both ends of the line support autonegotiation, we highly recommend the default setting of auto
negotiation.
•
If one interface supports autonegotiation and the other end does not, configure duplex and speed on
both interfaces; do not use the auto setting on the supported side.
•
When STP is enabled and a port is reconfigured, the switch can take up to 30 seconds to check for
loops. The port LED is amber while STP reconfigures.
Changing the interface speed and duplex mode configuration might shut down and re-enable the
interface during the reconfiguration.
Setting the Interface Speed and Duplex Parameters
Beginning in privileged EXEC mode, follow these steps to set the speed and duplex mode for a physical
interface.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Specify the physical interface to be configured, and enter interface
configuration mode.
Step 3
speed {10 | 100 | 1000 | auto [10 | 100 |
1000] | nonegotiate}
Enter the appropriate speed parameter for the interface:
•
Enter 10, 100, or 1000 to set a specific speed for the interface.
The 1000 keyword is available only for 10/100/1000 Mb/s ports
or SFP module ports with a 1000BASE-T SFP module.
•
Enter auto to enable the interface to autonegotiate speed with the
connected device. If you use the 10, 100, or the 1000 keywords
with the auto keyword, the port autonegotiates only at the
specified speeds.
•
The nonegotiate keyword is available but not supported on 10
GigabitEthernet ports. When a Cisco1000BASE-T SFP module is
in the SFP module slot, the speed can be configured to 10, 100,
1000, or to auto, but not to nonegotiate.
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Step 4
Command
Purpose
duplex {auto | full | half}
Enter the duplex parameter for the interface.
Enable half-duplex mode (for interfaces operating only at 10 or
100 Mb/s). You cannot configure half-duplex mode for interfaces
operating at 1000 Mb/s.
You can configure the duplex setting when the speed is set to auto.
This command is not available on 10 GigabitEthernet ports or on SFP
module ports with these exceptions:
Step 5
Step 6
Step 7
•
If a Cisco 1000BASE-T SFP module is inserted, you can
configure duplex to auto or to full.
•
If a Cisco 100BASE-FX SFP module is inserted, you can
configure duplex to full or to half. Although the auto keyword is
available, it puts the interface in half-duplex mode (the default).
end
Return to privileged EXEC mode.
show interfaces interface-id
Display the interface speed and duplex mode configuration.
copy running-config startup-config
(Optional) Save your entries in the configuration file.
Use the no speed and no duplex interface configuration commands to return the interface to the default
speed and duplex settings (autonegotiate). To return all interface settings to the defaults, use the default
interface interface-id interface configuration command.
This example shows how to set the interface speed to 10 Mb/s and the duplex mode to half:
Switch# configure terminal
Switch(config)# interface gigabitethernet0/3
Switch(config-if)# speed 10
Switch(config-if)# duplex half
This example shows how to set the interface speed to 100 Mb/s on a 10/100/1000 Mb/s port:
Switch# configure terminal
Switch(config)# interface gigabitethernet0/2
Switch(config-if)# speed 100
Configuring IEEE 802.3x Flow Control
IEEE 802.3x flow control enables connected Ethernet ports to control traffic rates during congestion by
allowing congested nodes to pause link operation at the other end. If one port experiences congestion
and cannot receive any more traffic, it notifies the other port by sending a pause frame to stop sending
until the condition clears. Upon receipt of a pause frame, the sending device stops sending any data
packets, which prevents any loss of data packets during the congestion period.
Note
Ports can receive, but not send, pause frames.
You use the flowcontrol interface configuration command to set the interface’s ability to receive pause
frames to on, off, or desired. The default state is off.
When set to desired, an interface can operate with an attached device that is required to send
flow-control packets or with an attached device that is not required to but can send flow-control packets.
These rules apply to IEEE 802.3x flow control settings on the device:
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Note
•
receive on (or desired): The port cannot send pause frames but can operate with an attached device
that is required to or can send pause frames; the port can receive pause frames.
•
receive off: IEEE 802.3x flow control does not operate in either direction. In case of congestion, no
indication is given to the link partner, and no pause frames are sent or received by either device.
For details on the command settings and the resulting IEEE 802.3x flow control resolution on local and
remote ports, see the flowcontrol interface configuration command in the command reference for this
release.
Beginning in privileged EXEC mode, follow these steps to configure IEEE 802.3x flow control on an
interface:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode
Step 2
interface interface-id
Specify the physical interface to be configured, and enter
interface configuration mode.
Step 3
flowcontrol {receive} {on | off | desired}
Configure the IEEE 802.3x flow control mode for the port.
Step 4
end
Return to privileged EXEC mode.
Step 5
show interfaces interface-id
Verify the interface IEEE 802.3x flow control settings.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.
To disable IEEE 802.3x flow control, use the flowcontrol receive off interface configuration command.
This example shows how to enable IEEE 802.3x flow control on a port:
Switch# configure terminal
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# flowcontrol receive on
Switch(config-if)# end
Configuring Auto-MDIX on an Interface
When automatic medium-dependent interface crossover (auto-MDIX) is enabled on an interface, the
interface automatically detects the required cable connection type (straight through or crossover) and
configures the connection appropriately. When connecting switches without the auto-MDIX feature, you
must use straight-through cables to connect to devices such as servers, workstations, or routers and
crossover cables to connect to other switches or repeaters. With auto-MDIX enabled, you can use either
type of cable to connect to other devices, and the interface automatically corrects for any incorrect
cabling. For more information about cabling requirements, see the hardware installation guide.
Auto-MDIX is enabled by default. When you enable auto-MDIX, you must also set the speed and duplex
on the interface to auto so that the feature operates correctly. Auto-MDIX is supported on all 10/100 and
10/100/1000 Mb/s interfaces and on Cisco 10/100/1000 BASE-T/TX SFP module interfaces. It is not
supported on 1000 BASE-SX or -LX SFP module interfaces.
Table 10-3 shows the link states that result from auto-MDIX settings and correct and incorrect cabling.
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Table 10-3
Link Conditions and Auto-MDIX Settings
Local Side Auto-MDIX
Remote Side Auto-MDIX With Correct Cabling
With Incorrect Cabling
On
On
Link up
Link up
On
Off
Link up
Link up
Off
On
Link up
Link up
Off
Off
Link up
Link down
Beginning in privileged EXEC mode, follow these steps to configure auto-MDIX on an interface:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode
Step 2
interface interface-id
Specify the physical interface to be configured, and enter interface
configuration mode.
Step 3
speed auto
Configure the interface to autonegotiate speed with the connected device.
Step 4
duplex auto
Configure the interface to autonegotiate duplex mode with the connected
device.
Step 5
mdix auto
Enable auto-MDIX on the interface.
Step 6
end
Return to privileged EXEC mode.
Step 7
show controllers ethernet-controller Verify the operational state of the auto-MDIX feature on the interface.
interface-id phy
Command is there, but no mdix in output.
Step 8
copy running-config startup-config
(Optional) Save your entries in the configuration file.
To disable auto-MDIX, use the no mdix auto interface configuration command.
This example shows how to enable auto-MDIX on a port:
Switch# configure terminal
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# speed auto
Switch(config-if)# duplex auto
Switch(config-if)# mdix auto
Switch(config-if)# end
Adding a Description for an Interface
You can add a description about an interface to help you remember its function. The description appears
in the output of these privileged EXEC commands: show configuration, show running-config, and
show interfaces.
Beginning in privileged EXEC mode, follow these steps to add a description for an interface:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Specify the interface for which you are adding a description, and enter
interface configuration mode.
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Command
Purpose
Step 3
description string
Add a description (up to 240 characters) for an interface.
Step 4
end
Return to privileged EXEC mode.
Step 5
show interfaces interface-id description Verify your entry.
or
show running-config
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.
Use the no description interface configuration command to delete the description.
This example shows how to add a description on a port and how to verify the description:
Switch# config terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface gigabitethernet0/2
Switch(config-if)# description Connects to Marketing
Switch(config-if)# end
Switch# show interfaces gigabitethernet0/2 description
Interface Status
Protocol Description
Gi 0/2
admin down
down
Connects to Marketing
Configuring Layer 3 Interfaces
The switch supports these types of Layer 3 interfaces:
•
SVIs: You should configure SVIs for any VLANs for which you want to route traffic. SVIs are
created when you enter a VLAN ID following the interface vlan global configuration command. To
delete an SVI, use the no interface vlan global configuration command. You cannot delete interface
VLAN 1.
Note
When you create an SVI, it does not become active until it is associated with a physical port.
For information about assigning Layer 2 ports to VLANs, see Chapter 11, “Configuring
VLANs.”
•
Routed ports: Routed ports are physical ports configured to be in Layer 3 mode by using the no
switchport interface configuration command.
•
Layer 3 EtherChannel ports: EtherChannel interfaces made up of routed ports.
EtherChannel port interfaces are described in Chapter 28, “Configuring EtherChannels.”
A Layer 3 switch can have an IP address assigned to each routed port and SVI.
There is no defined limit to the number of SVIs and routed ports that can be configured in a switch.
However, the interrelationship between the number of SVIs and routed ports and the number of other
features being configured might have an impact on CPU usage because of hardware limitations. If the
switch is using maximum hardware resources, attempts to create a routed port or SVI have these results:
•
If you try to create a new routed port, the switch generates a message that there are not enough
resources to convert the interface to a routed port, and the interface remains as a switch port.
•
If you try to create an extended-range VLAN, an error message is generated, and the extended-range
VLAN is rejected.
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•
If the switch attempts to boot up with a configuration that has more VLANs and routed ports than
hardware can support, the VLANs are created, but the routed ports are shut down, and the switch
sends a message that this was due to insufficient hardware resources.
All Layer 3 interfaces require an IP address to route traffic. This procedure shows how to configure an
interface as a Layer 3 interface and how to assign an IP address to an interface.
Note
If the physical port is in Layer 2 mode (the default), you must enter the no switchport interface
configuration command to put the interface into Layer 3 mode. Entering a no switchport command
disables and then re-enables the interface, which might generate messages on the device to which the
interface is connected. Furthermore, when you put an interface that is in Layer 2 mode into Layer 3
mode, the previous configuration information related to the affected interface might be lost, and the
interface is returned to its default configuration
Beginning in privileged EXEC mode, follow these steps to configure a Layer 3 interface:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface {gigabitethernet} interface-id} | {vlan vlan-id} Specify the interface to be configured as a Layer 3
| {port-channel port-channel-number}
interface, and enter interface configuration mode.
Step 3
no switchport
For physical ports only, enter Layer 3 mode.
Step 4
ip address ip_address subnet_mask
Configure the IP address and IP subnet.
Step 5
end
Return to privileged EXEC mode.
Step 6
show interfaces [interface-id]
Verify the configuration.
show ip interface [interface-id]
show running-config interface [interface-id]
Step 7
copy running-config startup-config
(Optional) Save your entries in the configuration file.
To remove an IP address from an interface, use the no ip address interface configuration command.
This example shows how to configure a port as a routed port and to assign it an IP address:
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# interface gigabitethernet0/2
Switch(config-if)# no switchport
Switch(config-if)# ip address 192.20.135.21 255.255.255.0
Configuring the Interface MTU
You can configure the maximum transmission unit (MTU) size on an interface to determine the packet
size that can be received on the interface. Because the switch does not fragment Layer 2 packets, it drops
switched Layer 2 packets larger than the packet size supported on the egress interface.
Beginning in privileged EXEC mode, follow these steps to change the MTU size on an interface:
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Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface-id
Specify the interface to be configured, and enter
interface configuration mode. The interface must be a
physical interface, but it can be one on which a service
instance is configured.
Step 3
mtu bytes
Configure the MTU size for the interface. The range is
from 1500 to 9800 bytes. The default is 1500.
Step 4
end
Return to privileged EXEC mode.
Step 5
show interface interface-id
Verify the configuration.
Step 6
copy running-config startup-config
Save your entries in the configuration file.
This example shows how to set the maximum packet size for a Gigabit Ethernet port to 1800 bytes:
Switch(config)# interface gigabitethernet0/3
Switch(config-if)# mtu 1800
Switch(config)# exit
Monitoring and Maintaining the Interfaces
These sections contain interface monitoring and maintenance information:
•
Monitoring Interface Status, page 10-21
•
Clearing and Resetting Interfaces and Counters, page 10-22
•
Shutting Down and Restarting the Interface, page 10-23
Monitoring Interface Status
Commands entered at the privileged EXEC prompt display information about the interface, including
the versions of the software and the hardware, the configuration, and statistics about the interfaces.
Table 10-4 lists some of these interface monitoring commands. (You can display the full list of show
commands by using the show ? command at the privileged EXEC prompt.) These commands are fully
described in the Cisco IOS Interface Command Reference, Release 12.2.
Table 10-4
Show Commands for Interfaces
Command
Purpose
show interfaces [interface-id]
Display the status and configuration of all interfaces or a specific
interface.
show interfaces interface-id status [err-disabled]
Display interface status or a list of interfaces in an error-disabled state.
show interfaces [interface-id] switchport
Display administrative and operational status of switching mode. You
can use this command to find out if a port is in routing or in switching
mode.
show interfaces [interface-id] description
Display the description configured on an interface or all interfaces and
the interface status.
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Table 10-4
Show Commands for Interfaces (continued)
Command
Purpose
show ip interface [interface-id]
Display the usability status of all interfaces configured for IP routing
or the specified interface.
show interface [interface-id] stats
Display the input and output packets by the switching path for the
interface.
show interfaces [interface-id] transceiver [detail | Display these physical and operational status about an SFP module:
dom-supported-list | module number | properties |
• interface-id–(Optional) Display configuration and status for a
threshold-table]
specified physical interface.
•
detail–(Optional) Display calibration properties, including high
and low numbers and any alarm information for any Digital
Optical Monitoring (DoM)-capable transceiver if one is installed
in the switch.
•
dom-supported-list–(Optional) List all supported DoM
transceivers.
•
module number–(Optional) Limit display to interfaces on module
on the switch. The range is 1 to 9. This option is not available if
you entered a specific interface ID.
•
properties–(Optional) Display speed, duplex, and inline power
settings on an interface
•
threshold-table–(Optional) Display alarm and warning threshold
table
show port-type [eni | nni | uni]
Display interface type information for the Cisco ME switch. The only
valid type is nni. Other keywords show no output.
show running-config interface [interface-id]
Display the running configuration in RAM for the interface.
show version
Display the hardware configuration, software version, the names and
sources of configuration files, and the boot images.
show controllers ethernet-controller interface-id
phy
Display the operational state of the auto-MDIX feature on the
interface. - Doesn’t seem to show this
Clearing and Resetting Interfaces and Counters
Table 10-5 lists the privileged EXEC mode clear commands that you can use to clear counters and reset
interfaces.
Table 10-5
Clear Commands for Interfaces
Command
Purpose
clear counters [interface-id]
Clear interface counters.
clear interface interface-id
Reset the hardware logic on an interface.
clear line [number | console 0 | vty number]
Reset the hardware logic on an asynchronous serial line.
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To clear the interface counters shown by the show interfaces privileged EXEC command, use the clear
counters privileged EXEC command. The clear counters command clears all current interface counters
from the interface unless you specify optional arguments that clear only a specific interface type from a
specific interface number.
Note
The clear counters privileged EXEC command does not clear counters retrieved by using Simple
Network Management Protocol (SNMP), but only those seen with the show interface privileged EXEC
command.
Shutting Down and Restarting the Interface
Shutting down an interface disables all functions on the specified interface and marks the interface as
unavailable on all monitoring command displays. This information is communicated to other network
servers through all dynamic routing protocols. The interface is not mentioned in any routing updates.
Beginning in privileged EXEC mode, follow these steps to shut down an interface:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface {vlan vlan-id} | {gigabitethernet interface-id} |
{port-channel port-channel-number}
Select the interface to be configured.
Step 3
shutdown
Shut down an interface.
Step 4
end
Return to privileged EXEC mode.
Step 5
show running-config
Verify your entry.
Use the no shutdown interface configuration command to enable an interface.
To verify that an interface is disabled, enter the show interfaces privileged EXEC command. A disabled
interface is shown as administratively down in the display.
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