Cisco Nexus 9000 NX-OS network device Configuration guide
The Cisco NX-OS device Nexus 9000 Series is a network device that is designed to support Open Shortest Path First version 2 (OSPFv2) for IPv4 networks. OSPFv2 is a link-state protocol that is used to build a routing table for the network. This device sends "hello" messages to discover other routers on the network. Once a neighbor is discovered, the routers connect to each other, compare information in the "hello" packet, and synchronize their link-state databases.
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C H A P T E R
5
Configuring OSPFv2
This chapter describes how to configure Open Shortest Path First version 2 (OSPFv2) for IPv4 networks on the Cisco NX-OS device.
This chapter includes the following sections:
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Licensing Requirements for OSPFv2, page 5-13
Prerequisites for OSPFv2, page 5-13
Guidelines and Limitations for OSPFv2, page 5-13
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Configuring Basic OSPFv2, page 5-14
Configuring Advanced OSPFv2, page 5-24
Verifying the OSPFv2 Configuration, page 5-48
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Configuration Examples for OSPFv2, page 5-49
Additional References, page 5-50
About OSPFv2
OSPFv2 is an IETF link-state protocol (see the “Link-State Protocols” section on page 1-9 ) for IPv4 networks. An OSPFv2 router sends a special message, called a hello packet, out each OSPF-enabled interface to discover other OSPFv2 neighbor routers. Once a neighbor is discovered, the two routers compare information in the Hello packet to determine if the routers have compatible configurations. The neighbor routers try to establish adjacency, which means that the routers synchronize their link-state databases to ensure that they have identical OSPFv2 routing information. Adjacent routers share link-state advertisements (LSAs) that include information about the operational state of each link, the cost of the link, and any other neighbor information. The routers then flood these received LSAs out every OSPF-enabled interface so that all OSPFv2 routers eventually have identical link-state databases.
When all OSPFv2 routers have identical link-state databases, the network is converged (see the
“Convergence” section on page 1-6 ). Each router then uses Dijkstra’s Shortest Path First (SPF) algorithm to build its route table.
You can divide OSPFv2 networks into areas. Routers send most LSAs only within one area, which reduces the CPU and memory requirements for an OSPF-enabled router.
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Chapter 5 Configuring OSPFv2
About OSPFv2
OSPFv2 supports IPv4, while OSPFv3 supports IPv6. For more information, see Chapter 6,
“Configuring OSPFv3.”
Note
OSPFv2 on Cisco NX-OS supports RFC 2328. This RFC introduced a different method to calculate route summary costs which is not compatible with the calculation used by RFC 1583. RFC 2328 also introduced different selection criteria for AS-external paths. It is important to ensure that all routers support the same RFC. Use the rfc1583compatibility command if your network includes routers that are only compliant with RFC 1583. The default supported RFC standard for OSPFv2 might be different for Cisco NX-OS and Cisco IOS. You must make adjustments to set the values identically. See the
“OSPF RFC Compatibility Mode Example” section on page 5-50
for more information.
This section includes the following topics:
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Link-State Advertisements, page 5-5
OSPFv2 and the Unicast RIB, page 5-7
Hello Packet
OSPFv2 routers periodically send Hello packets on every OSPF-enabled interface. The hello interval determines how frequently the router sends these Hello packets and is configured per interface. OSPFv2 uses Hello packets for the following tasks:
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Neighbor discovery
Keepalives
Bidirectional communications
Designated router election (see the
“Designated Routers” section on page 5-3
)
The Hello packet contains information about the originating OSPFv2 interface and router, including the assigned OSPFv2 cost of the link, the hello interval, and optional capabilities of the originating router.
An OSPFv2 interface that receives these Hello packets determines if the settings are compatible with the receiving interface settings. Compatible interfaces are considered neighbors and are added to the
neighbor table (see the “Neighbors” section on page 5-3
).
Hello packets also include a list of router IDs for the routers that the originating interface has communicated with. If the receiving interface sees its own router ID in this list, bidirectional communication has been established between the two interfaces.
OSPFv2 uses Hello packets as a keepalive message to determine if a neighbor is still communicating. If a router does not receive a Hello packet by the configured dead interval (usually a multiple of the hello interval), then the neighbor is removed from the local neighbor table.
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About OSPFv2
Neighbors
An OSPFv2 interface must have a compatible configuration with a remote interface before the two can be considered neighbors. The two OSPFv2 interfaces must match the following criteria:
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Hello interval
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Dead interval
Area ID (see the “Areas” section on page 5-4
)
Authentication
Optional capabilities
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If there is a match, the following information is entered into the neighbor table:
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Neighbor ID—The router ID of the neighbor.
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Priority—Priority of the neighbor. The priority is used for designated router election (see the
“Designated Routers” section on page 5-3 ).
State—Indication of whether the neighbor has just been heard from, is in the process of setting up bidirectional communications, is sharing the link-state information, or has achieved full adjacency.
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Dead time—Indication of the time since the last Hello packet was received from this neighbor.
IP Address—The IP address of the neighbor.
Designated Router—Indication of whether the neighbor has been declared as the designated router or as the backup designated router (see the
“Designated Routers” section on page 5-3
).
Local interface—The local interface that received the Hello packet for this neighbor.
Adjacency
Not all neighbors establish adjacency. Depending on the network type and designated router establishment, some neighbors become fully adjacent and share LSAs with all their neighbors, while other neighbors do not. For more information, see the
“Designated Routers” section on page 5-3
.
Adjacency is established using Database Description packets, Link State Request packets, and Link
State Update packets in OSPF. The Database Description packet includes just the LSA headers from the link-state database of the neighbor (see the
“Link-State Database” section on page 5-7
). The local router compares these headers with its own link-state database and determines which LSAs are new or updated.
The local router sends a Link State Request packet for each LSA that it needs new or updated information on. The neighbor responds with a Link State Update packet. This exchange continues until both routers have the same link-state information.
Designated Routers
Networks with multiple routers present a unique situation for OSPF. If every router floods the network with LSAs, the same link-state information is sent from multiple sources. Depending on the type of network, OSPFv2 might use a single router, the designated router (DR), to control the LSA floods and
represent the network to the rest of the OSPFv2 area (see the “Areas” section on page 5-4
). If the DR fails, OSPFv2 selects a backup designated router (BDR). If the DR fails, OSPFv2 uses the BDR.
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About OSPFv2
Chapter 5 Configuring OSPFv2
Network types are as follows:
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Point-to-point—A network that exists only between two routers. All neighbors on a point-to-point network establish adjacency and there is no DR.
Broadcast—A network with multiple routers that can communicate over a shared medium that allows broadcast traffic, such as Ethernet. OSPFv2 routers establish a DR and BDR that controls
LSA flooding on the network. OSPFv2 uses the well-known IPv4 multicast addresses 224.0.0.5 and a MAC address of 0100.5300.0005 to communicate with neighbors.
The DR and BDR are selected based on the information in the Hello packet. When an interface sends a
Hello packet, it sets the priority field and the DR and BDR field if it knows who the DR and BDR are.
The routers follow an election procedure based on which routers declare themselves in the DR and BDR fields and the priority field in the Hello packet. As a final tie breaker, OSPFv2 chooses the highest router
IDs as the DR and BDR.
All other routers establish adjacency with the DR and the BDR and use the IPv4 multicast address
224.0.0.6 to send LSA updates to the DR and BDR.
Figure 5-1 shows this adjacency relationship
between all routers and the DR.
DRs are based on a router interface. A router might be the DR for one network and not for another network on a different interface.
Figure 5-1 DR in Multi-Access Network
Router A Router B Router C
Router D or DR
Router E
= Multi-access network
= Logical connectivity to Designated Router for OSPF
Areas
You can limit the CPU and memory requirements that OSPFv2 puts on the routers by dividing an
OSPFv2 network into areas. An area is a logical division of routers and links within an OSPFv2 domain that creates separate subdomains. LSA flooding is contained within an area, and the link-state database is limited to links within the area. You can assign an area ID to the interfaces within the defined area.
The Area ID is a 32-bit value that you can enter as a number or in dotted decimal notation, such as
10.2.3.1.
Cisco NX-OS always displays the area in dotted decimal notation.
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About OSPFv2
If you define more than one area in an OSPFv2 network, you must also define the backbone area, which has the reserved area ID of 0. If you have more than one area, then one or more routers become area border routers (ABRs). An ABR connects to both the backbone area and at least one other defined area
).
Figure 5-2 OSPFv2 Areas
ABR1
Area 0
Area 3
Area 5
ABR2
The ABR has a separate link-state database for each area to which it connects. The ABR sends Network
Summary (type 3) LSAs (see the
“Route Summarization” section on page 5-10
) from one connected area to the backbone area. The backbone area sends summarized information about one area to another area.
In
Figure 5-2 , Area 0 sends summarized information about Area 5 to Area 3.
OSPFv2 defines one other router type: the autonomous system boundary router (ASBR). This router connects an OSPFv2 area to another autonomous system. An autonomous system is a network controlled by a single technical administration entity. OSPFv2 can redistribute its routing information into another autonomous system or receive redistributed routes from another autonomous system. For more information, see the
“Advanced Features” section on page 5-8
.
Link-State Advertisements
OSPFv2 uses link-state advertisements (LSAs) to build its routing table.
This section includes the following topics:
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Flooding and LSA Group Pacing, page 5-6
LSA Types
shows the LSA types supported by Cisco NX-OS.
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Table 5-1 LSA Types
Type Name
1
2
3
4
Router LSA
Description
LSA sent by every router. This LSA includes the state and the cost of all links and a list of all OSPFv2 neighbors on the link. Router LSAs trigger an
SPF recalculation. Router LSAs are flooded to local OSPFv2 area.
Network LSA LSA sent by the DR. This LSA lists all routers in the multi-access network.
Network LSAs trigger an SPF recalculation. See the
“Designated Routers” section on page 5-3 .
Network
Summary LSA
LSA sent by the area border router to an external area for each destination in the local area. This LSA includes the link cost from the area border router
to the local destination. See the “Areas” section on page 5-4
.
ASBR Summary
LSA
LSA sent by the area border router to an external area. This LSA advertises the link cost to the ASBR only. See the
.
5 AS External
LSA
LSA generated by the ASBR. This LSA includes the link cost to an external autonomous system destination. AS External LSAs are flooded throughout the autonomous system. See the
7 NSSA External
LSA
LSA generated by the ASBR within a not-so-stubby area (NSSA). This LSA includes the link cost to an external autonomous system destination. NSSA
External LSAs are flooded only within the local NSSA. See the “Areas” section on page 5-4 .
9–11 Opaque LSAs LSA used to extend OSPF. See the
“Opaque LSAs” section on page 5-7
.
Link Cost
Each OSPFv2 interface is assigned a link cost. The cost is an arbitrary number. By default, Cisco NX-OS assigns a cost that is the configured reference bandwidth divided by the interface bandwidth. By default, the reference bandwidth is 40 Gb/s. The link cost is carried in the LSA updates for each link.
Flooding and LSA Group Pacing
When an OSPFv2 router receives an LSA, it forwards that LSA out every OSPF-enabled interface, flooding the OSPFv2 area with this information. This LSA flooding guarantees that all routers in the network have identical routing information. LSA flooding depends on the OSPFv2 area configuration
(see the “Areas” section on page 5-4
). The LSAs are flooded based on the link-state refresh time (every
30 minutes by default). Each LSA has its own link-state refresh time.
You can control the flooding rate of LSA updates in your network by using the LSA group pacing feature. LSA group pacing can reduce high CPU or buffer usage. This feature groups LSAs with similar link-state refresh times to allow OSPFv2 to pack multiple LSAs into an OSPFv2 Update message.
By default, LSAs with link-state refresh times within 10 seconds of each other are grouped together. You should lower this value for large link-state databases or raise it for smaller databases to optimize the
OSPFv2 load on your network.
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About OSPFv2
Link-State Database
Each router maintains a link-state database for the OSPFv2 network. This database contains all the collected LSAs, and includes information on all the routes through the network. OSPFv2 uses this information to calculate the best path to each destination and populates the routing table with these best paths.
LSAs are removed from the link-state database if no LSA update has been received within a set interval, called the MaxAge. Routers flood a repeat of the LSA every 30 minutes to prevent accurate link-state information from being aged out. Cisco NX-OS supports the LSA grouping feature to prevent all LSAs from refreshing at the same time. For more information, see the
“Flooding and LSA Group Pacing” section on page 5-6 .
Opaque LSAs
Opaque LSAs allow you to extend OSPF functionality. Opaque LSAs consist of a standard LSA header followed by application-specific information. This information might be used by OSPFv2 or by other
applications. OSPFv2 uses Opaque LSAs to support OSPFv2 Graceful Restart capability (see the “High
Availability and Graceful Restart” section on page 5-11
). Three Opaque LSA types are defined as follows:
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•
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LSA type 9—Flooded to the local network.
LSA type 10—Flooded to the local area.
LSA type 11—Flooded to the local autonomous system.
OSPFv2 and the Unicast RIB
OSPFv2 runs the Dijkstra shortest path first algorithm on the link-state database. This algorithm selects the best path to each destination based on the sum of all the link costs for each link in the path. The resultant shortest path for each destination is then put in the OSPFv2 route table. When the OSPFv2 network is converged, this route table feeds into the unicast Routing Information Base (RIB). OSPFv2 communicates with the unicast RIB to do the following:
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Add or remove routes
Handle route redistribution from other protocols
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Provide convergence updates to remove stale OSPFv2 routes and for stub router advertisements (see the
“OSPFv2 Stub Router Advertisements” section on page 5-12 )
OSPFv2 also runs a modified Dijkstra algorithm for fast recalculation for summary and external (type
3, 4, 5, and 7) LSA changes.
Authentication
You can configure authentication on OSPFv2 messages to prevent unauthorized or invalid routing updates in your network. Cisco NX-OS supports the following authentication methods:
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Simple password authentication
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Cryptographic authentication
You can configure the OSPFv2 authentication for an OSPFv2 area or per interface.
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Simple Password Authentication
Simple password authentication uses a simple cleartext password that is sent as part of the OSPFv2 message. The receiving OSPFv2 router must be configured with the same cleartext password to accept the OSPFv2 message as a valid route update. Because the password is in cleartext, anyone who can watch traffic on the network can learn the password.
Cryptographic Authentication
Cryptographic authentication uses an encrypted password for OSPFv2 authentication. The transmitter computes a code using the packet to be transmitted and the key string, inserts the code and the key ID in the packet, and transmits the packet. The receiver validates the code in the packet by computing the code locally using the received packet and the key string (corresponding to the key ID in the packet) configured locally.
Both message digest 5 (MD5) and hash-based message authentication code secure hash algorithm
(HMAC-SHA) cryptographic authentication are supported.
MD5 Authentication
You can use MD5 authentication to authenticate OSPFv2 messages by configuring a password that is shared at the local router and all remote OSPFv2 neighbors. For each OSPFv2 message, Cisco NX-OS creates an MD5 one-way message digest based on the message itself and the encrypted password. The interface sends this digest with the OSPFv2 message. The receiving OSPFv2 neighbor validates the digest using the same encrypted password. If the message has not changed, the digest calculation is identical, and the OSPFv2 message is considered valid.
MD5 authentication includes a sequence number with each OSPFv2 message to ensure that no message is replayed in the network.
HMAC-SHA Authentication
Starting with Cisco NX-OS Release 7.0(3)I3(1), OSPFv2 supports RFC 5709 to allow the use of
HMAC-SHA algorithms, which offer more security than MD5. The HMAC-SHA-1, HMAC-SHA-256,
HMAC-SHA-384. and HMAC-SHA-512 algorithms are supported for OSPFv2 authentication.
Advanced Features
Cisco NX-OS supports advanced OSPFv2 features that enhance the usability and scalability of OSPFv2 in the network. This section includes the following topics:
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Route Redistribution, page 5-10
Route Summarization, page 5-10
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High Availability and Graceful Restart, page 5-11
OSPFv2 Stub Router Advertisements, page 5-12
Multiple OSPFv2 Instances, page 5-12
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Stub Area
About OSPFv2
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Virtualization Support, page 5-12
You can limit the amount of external routing information that floods an area by making it a stub area. A stub area is an area that does not allow AS External (type 5) LSAs (see the
propagate external route information. Stub areas have the following requirements:
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All routers in the stub area are stub routers. See the
No ASBR routers exist in the stub area.
“Stub Routing” section on page 1-7 .
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You cannot configure virtual links in the stub area.
Figure 5-3 shows an example of an OSPFv2 autonomous system where all routers in area 0.0.0.10 have
to go through the ABR to reach external autonomous systems. Area 0.0.0.10 can be configured as a stub area.
Figure 5-3 Stub Area
ABR
Backbone Area 10
Stub area
ASBR
Stub areas use a default route for all traffic that must go through the backbone area to the external autonomous system. The default route is 0.0.0.0 for IPv4.
Not-So-Stubby Area
A Not-so-Stubby Area (NSSA) is similar to a stub area, except that an NSSA allows you to import autonomous system external routes within an NSSA using redistribution. The NSSA ASBR redistributes these routes and generates NSSA External (type 7) LSAs that it floods throughout the NSSA. You can optionally configure the ABR that connects the NSSA to other areas to translate this NSSA External LSA to AS External (type 5) LSAs. The ABR then floods these AS External LSAs throughout the OSPFv2 autonomous system. Summarization and filtering are supported during the translation. See the
“Link-State Advertisements” section on page 5-5
for information about NSSA External LSAs.
You can, for example, use NSSA to simplify administration if you are connecting a central site using
OSPFv2 to a remote site that is using a different routing protocol. Before NSSA, the connection between the corporate site border router and a remote router could not be run as an OSPFv2 stub area because routes for the remote site could not be redistributed into a stub area. With NSSA, you can extend OSPFv2 to cover the remote connection by defining the area between the corporate router and remote router as an NSSA (see the
“Configuring NSSA” section on page 5-28
).
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The backbone Area 0 cannot be an NSSA.
Virtual Links
Virtual links allow you to connect an OSPFv2 area ABR to a backbone area ABR when a direct physical connection is not available.
shows a virtual link that connects Area 3 to the backbone area through Area 5.
Figure 5-4 Virtual Links
Area 0
ABR1
ABR2
Area 5
Area 3
You can also use virtual links to temporarily recover from a partitioned area, which occurs when a link within the area fails, isolating part of the area from reaching the designated ABR to the backbone area.
Route Redistribution
OSPFv2 can learn routes from other routing protocols by using route redistribution. See the “Route
Redistribution” section on page 1-6 . You configure OSPFv2 to assign a link cost for these redistributed routes or a default link cost for all redistributed routes.
Route redistribution uses route maps to control which external routes are redistributed. You must configure a route map with the redistribution to control which routes are passed into OSPFv2. A route map allows you to filter routes based on attributes such as the destination, origination protocol, route type, route tag, and so on. You can use route maps to modify parameters in the AS External (type 5) and
NSSA External (type 7) LSAs before these external routes are advertised in the local OSPFv2 autonomous system. See Chapter 15, “Configuring Route Policy Manager,” for information about configuring route maps.
Route Summarization
Because OSPFv2 shares all learned routes with every OSPF-enabled router, you might want to use route summarization to reduce the number of unique routes that are flooded to every OSPF-enabled router.
Route summarization simplifies route tables by replacing more-specific addresses with an address that represents all the specific addresses. For example, you can replace 10.1.1.0/24, 10.1.2.0/24, and
10.1.3.0/24 with one summary address, 10.1.0.0/16.
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Typically, you would summarize at the boundaries of area border routers (ABRs). Although you could configure summarization between any two areas, it is better to summarize in the direction of the backbone so that the backbone receives all the aggregate addresses and injects them, already summarized, into other areas. The two types of summarization are as follows:
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Inter-area route summarization
External route summarization
You configure inter-area route summarization on ABRs, summarizing routes between areas in the autonomous system. To take advantage of summarization, you should assign network numbers in areas in a contiguous way to be able to lump these addresses into one range.
External route summarization is specific to external routes that are injected into OSPFv2 using route redistribution. You should make sure that external ranges that are being summarized are contiguous.
Summarizing overlapping ranges from two different routers could cause packets to be sent to the wrong destination. Configure external route summarization on ASBRs that are redistributing routes into OSPF.
When you configure a summary address, Cisco NX-OS automatically configures a discard route for the summary address to prevent routing black holes and route loops.
High Availability and Graceful Restart
Cisco NX-OS provides a multilevel high-availability architecture. OSPFv2 supports stateful restart, which is also referred to as non-stop routing (NSR). If OSPFv2 experiences problems, it attempts to restart from its previous run-time state. The neighbors do not register any neighbor event in this case. If the first restart is not successful and another problem occurs, OSPFv2 attempts a graceful restart.
A graceful restart, or nonstop forwarding (NSF), allows OSPFv2 to remain in the data forwarding path through a process restart. When OSPFv2 needs to perform a graceful restart, it sends a link-local opaque
(type 9) LSA, called a grace LSA (see the
“Opaque LSAs” section on page 5-7 ). This restarting OSPFv2
platform is called NSF capable.
The grace LSA includes a grace period, which is a specified time that the neighbor OSPFv2 interfaces hold onto the LSAs from the restarting OSPFv2 interface. (Typically, OSPFv2 tears down the adjacency and discards all LSAs from a down or restarting OSPFv2 interface.) The participating neighbors, which are called NSF helpers, keep all LSAs that originate from the restarting OSPFv2 interface as if the interface was still adjacent.
When the restarting OSPFv2 interface is operational again, it rediscovers its neighbors, establishes adjacency, and starts sending its LSA updates again. At this point, the NSF helpers recognize that the graceful restart has finished.
Stateful restart is used in the following scenarios:
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•
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First recovery attempt after the process experiences problems
User-initiated switchover using the system switchover command
Graceful restart is used in the following scenarios:
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Second recovery attempt after the process experiences problems within a 4-minute interval
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Manual restart of the process using the restart ospf command
Active supervisor removal
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Active supervisor reload using the reload module active-sup command
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OSPFv2 Stub Router Advertisements
You can configure an OSPFv2 interface to act as a stub router using the OSPFv2 Stub Router
Advertisements feature. Use this feature when you want to limit the OSPFv2 traffic through this router, such as when you want to introduce a new router to the network in a controlled manner or limit the load on a router that is already overloaded. You might also want to use this feature for various administrative or traffic engineering reasons.
OSPFv2 stub router advertisements do not remove the OSPFv2 router from the network topology, but they do prevent other OSPFv2 routers from using this router to route traffic to other parts of the network.
Only the traffic that is destined for this router or directly connected to this router is sent.
OSPFv2 stub router advertisements mark all stub links (directly connected to the local router) to the cost of the local OSPFv2 interface. All remote links are marked with the maximum cost (0xFFFF).
Multiple OSPFv2 Instances
Cisco NX-OS supports multiple instances of the OSPFv2 protocol that run on the same node. You cannot configure multiple instances over the same interface. By default, every instance uses the same system router ID. You must manually configure the router ID for each instance if the instances are in the same
OSPFv2 autonomous system. For the number of supported OSPFv2 instances, see the Cisco Nexus 9000
Series NX-OS Verified Scalability Guide.
SPF Optimization
Cisco NX-OS optimizes the SPF algorithm in the following ways:
•
•
Partial SPF for Network (type 2) LSAs, Network Summary (type 3) LSAs, and AS External (type
5) LSAs—When there is a change on any of these LSAs, Cisco NX-OS performs a faster partial calculation rather than running the whole SPF calculation.
SPF timers—You can configure different timers for controlling SPF calculations. These timers include exponential backoff for subsequent SPF calculations. The exponential backoff limits the
CPU load of multiple SPF calculations.
BFD
This feature supports bidirectional forwarding detection (BFD) for IPv4. BFD is a detection protocol that provides fast forwarding-path failure detection times. BFD provides subsecond failure detection between two adjacent devices and can be less CPU-intensive than protocol hello messages because some of the BFD load can be distributed onto the data plane on supported modules. See the Cisco Nexus 9000
Series NX-OS Interfaces Configuration Guide for more information.
Virtualization Support
Cisco NX-OS supports multiple process instances for OSPFv2. Each OSPFv2 instance can support multiple virtual routing and forwarding (VRF) instances, up to the system limit. For the number of supported OSPFv2 instances, see the Cisco Nexus 9000 Series NX-OS Verified Scalability Guide.
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Licensing Requirements for OSPFv2
Licensing Requirements for OSPFv2
The following table shows the licensing requirements for this feature:
Product License Requirement
Cisco NX-OS OSPFv2 requires an Enterprise Services license. For a complete explanation of the Cisco NX-OS licensing scheme and how to obtain and apply licenses, see the Cisco NX-OS Licensing Guide.
Prerequisites for OSPFv2
OSPFv2 has the following prerequisites:
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You must be familiar with routing fundamentals to configure OSPF.
You are logged on to the switch.
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You have configured at least one interface for IPv4 that can communicate with a remote OSPFv2 neighbor.
You have installed the Enterprise Services license.
•
You have completed the OSPFv2 network strategy and planning for your network. For example, you must decide whether multiple areas are required.
You have enabled the OSPF feature (see the
“Enabling OSPFv2” section on page 5-15
).
Guidelines and Limitations for OSPFv2
OSPFv2 has the following configuration guidelines and limitations:
•
•
Cisco NX-OS displays areas in dotted decimal notation regardless of whether you enter the area in decimal or dotted decimal notation.
All OSPFv2 routers must operate in the same RFC compatibility mode. OSPFv2 for Cisco NX-OS complies with RFC 2328. Use the rfc1583compatibility command in router configuration mode if your network includes routers that support only RFC 1583.
•
•
In scaled scenarios, when the number of interfaces and link-state advertisements in an OSPF process is large, the snmp-walk on OSPF MIB objects is expected to time out with a small-values timeout at the SNMP agent. If your observe a timeout on the querying SNMP agent while polling OSPF MIB objects, increase the timeout value on the polling SNMP agent.
The following guidelines and limitations apply to the administrative distance feature:
–
–
When an OSPF route has two or more equal cost paths, configuring the administrative distance is nondeterministic for the match ip route-source command.
Configuring the administrative distance is supported only for the match route-type, match ip
address prefix-list, and match ip route-source prefix-list commands. The other match statements are ignored.
–
There is no preference among the match route-type, match ip address, and match ip
route-source commands for setting the administrative distance of OSPF routes. In this way, the behavior of the table map for setting the administrative distance in Cisco NX-OS OSPF is different from that in Cisco IOS OSPF.
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Default Settings
•
•
–
The discard route is always assigned an administrative distance of 220. No configuration in the table map applies to OSPF discard routes.
If you configure the delay restore seconds command in vPC configuration mode and if the VLANs on the multichassis EtherChannel trunk (MCT) are announced by OSPFv2 or OSPFv3 using switch virtual interfaces (SVIs), those SVIs are announced with MAX_LINK_COST on the vPC secondary node for the duration of the configured time. As a result, all route or host programming completes after the vPC synchronization operation (on a peer reload of the secondary vPC node) before attracting traffic. This behavior allows for minimal packet loss for any north-to-south traffic.
For N9K-X9636C-R and N9K-X9636Q-R line cards and the N9K-C9508-FM-R fabric module, the output of the show run ospf command might show the default values for some OSPF commands.
Note
If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.
Default Settings
Table 5-2 lists the default settings for OSPFv2 parameters.
Table 5-2 Default OSPFv2 Parameters
Parameters
Administrative distance
Hello interval
Dead interval
Discard routes
Graceful restart grace period
OSPFv2 feature
Stub router advertisement announce time
Reference bandwidth for link cost calculation
LSA minimal arrival time
LSA group pacing
SPF calculation initial delay time
SPF minimum hold time
SPF calculation initial delay time
Default
110
10 seconds
40 seconds
Enabled
60 seconds
Disabled
600 seconds
40 Gb/s
1000 milliseconds
10 seconds
200 milliseconds
5000 milliseconds
1000 milliseconds
Configuring Basic OSPFv2
Configure OSPFv2 after you have designed your OSPFv2 network.
This section includes the following topics:
•
•
Creating an OSPFv2 Instance, page 5-16
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•
•
•
•
Configuring Optional Parameters on an OSPFv2 Instance, page 5-17
Configuring Networks in OSPFv2, page 5-18
Configuring Authentication for an Area, page 5-20
Configuring Authentication for an Interface, page 5-21
Enabling OSPFv2
You must enable the OSPFv2 feature before you can configure OSPFv2.
SUMMARY STEPS
3.
4.
1.
2.
configure terminal feature ospf
(Optional) show feature
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 feature ospf
Example:
switch(config)# feature ospf
Step 3 show feature
Example:
switch(config)# show feature
Step 4 copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
Purpose
Enters global configuration mode.
Enables the OSPFv2 feature.
(Optional) Displays enabled and disabled features.
(Optional) Saves this configuration change.
To disable the OSPFv2 feature and remove all associated configuration, use the no feature ospf command in global configuration mode:
Command no feature ospf
Example:
switch(config)# no feature ospf
Purpose
Disables the OSPFv2 feature and removes all associated configuration.
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Configuring Basic OSPFv2
Creating an OSPFv2 Instance
The first step in configuring OSPFv2 is to create an OSPFv2 instance. You assign a unique instance tag for this OSPFv2 instance. The instance tag can be any string.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the
“Enabling OSPFv2” section on page 5-15
).
Use the show ip ospf instance-tag command to verify that the instance tag is not in use.
OSPFv2 must be able to obtain a router identifier (for example, a configured loopback address) or you must configure the router ID option.
SUMMARY STEPS
1.
2.
3.
4.
5.
configure terminal
router ospf instance-tag
router-id ip-address
(Optional) show ip ospf instance-tag
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 router-id
ip-address
Example:
switch(config-router)# router-id
192.0.2.1
Step 4 show ip ospf
instance-tag
Example
: switch(config-router)# show ip ospf 201
Step 5 copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
Purpose
Enters global configuration mode.
Creates a new OSPFv2 instance with the configured instance tag.
(Optional) Configures the OSPFv2 router ID. This IP address identifies this OSPFv2 instance and must exist on a configured interface in the system.
(Optional) Displays OSPF information.
(Optional) Saves this configuration change.
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To remove the OSPFv2 instance and all associated configuration, use the no router ospf command in global configuration mode.
Command no router ospf
instance-tag
Example:
switch(config)# no router ospf 201
Purpose
Deletes the OSPF instance and the associated configuration.
Note
This command does not remove the OSPF configuration in interface mode. You must manually remove any OSPFv2 commands configured in interface mode.
Configuring Optional Parameters on an OSPFv2 Instance
You can configure optional parameters for OSPF.
For more information about OSPFv2 instance parameters, see the
“Configuring Advanced OSPFv2” section on page 5-24 .
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the
“Enabling OSPFv2” section on page 5-15 ).
OSPFv2 must be able to obtain a router identifier (for example, a configured loopback address) or you must configure the router ID option.
DETAILED STEPS
You can configure the following optional parameters for OSPFv2 in router configuration mode:
Command distance
number
Example:
switch(config-router)# distance 25
log-adjacency-changes
[detail]
Example:
switch(config-router)# log-adjacency-changes
maximum-paths
path-number
Example:
switch(config-router)# maximum-paths 4
passive-interface default
Example:
switch(config-router)# passive-interface default
Purpose
Configures the administrative distance for this
OSPFv2 instance. The range is from 1 to 255. The default is 110.
Generates a system message whenever a neighbor changes state.
Configures the maximum number of equal OSPFv2 paths to a destination in the route table. This command is used for load balancing. The range is from 1 to 64. The default is 8.
Suppresses routing updates on all interfaces. This command is overridden by the VRF or interface command mode configuration.
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This example shows how to create an OSPFv2 instance: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# copy running-config startup-config
Configuring Networks in OSPFv2
You can configure a network to OSPFv2 by associating it through the interface that the router uses to connect to that network (see the
“Neighbors” section on page 5-3 ). You can add all networks to the
default backbone area (Area 0), or you can create new areas using any decimal number or an IP address.
Note
All areas must connect to the backbone area either directly or through a virtual link.
Note
OSPF is not enabled on an interface until you configure a valid IP address for that interface.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the
“Enabling OSPFv2” section on page 5-15
).
SUMMARY STEPS
3.
4.
1.
2.
5.
6.
configure terminal
interface interface-type slot/port
ip address ip-prefix/length
ip router ospf instance-tag area area-id [secondaries none]
(Optional) show ip ospf instance-tag interface interface-type slot/port
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 interface
interface-type slot/port
Example:
switch(config)# interface ethernet 1/2 switch(config-if)#
Step 3 ip address
ip-prefix/length
Example:
switch(config-if)# ip address
192.0.2.1/16
Purpose
Enters global configuration mode.
Enters interface configuration mode.
Assigns an IP address and subnet mask to this interface.
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Command Purpose
Step 4 ip router ospf
instance-tag area area-id
[secondaries none]
Adds the interface to the OSPFv2 instance and area.
Example:
switch(config-if)# ip router ospf 201 area 0.0.0.15
Step 5 show ip ospf
instance-tag interface
interface-type slot/port
Example
: switch(config-if)# show ip ospf 201 interface ethernet 1/2
Step 6 copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
(Optional) Displays OSPF information.
(Optional) Saves this configuration change.
You can configure the following optional parameters for OSPFv2 in interface configuration mode:
Command ip ospf cost
number
Example:
switch(config-if)# ip ospf cost 25
ip ospf dead-interval
seconds
Purpose
Configures the OSPFv2 cost metric for this interface. The default is to calculate cost metric, based on the reference bandwidth and interface bandwidth. The range is from 1 to 65535.
Configures the OSPFv2 dead interval, in seconds.
The range is from 1 to 65535. The default is four times the hello interval, in seconds.
Example:
switch(config-if)# ip ospf dead-interval
50
ip ospf hello-interval
seconds
Example:
switch(config-if)# ip ospf hello-interval
25
ip ospf mtu-ignore
Example:
switch(config-if)# ip ospf mtu-ignore
[default | no] ip ospf passive-interface
Example:
switch(config-if)# ip ospf passive-interface
ip ospf priority
number
Example:
switch(config-if)# ip ospf priority 25
ip ospf shutdown
Configures the OSPFv2 hello interval, in seconds.
The range is from 1 to 65535. The default is 10 seconds.
Configures OSPFv2 to ignore any IP MTU mismatch with a neighbor. The default is to not establish adjacency if the neighbor MTU does not match the local interface MTU.
Suppresses routing updates on the interface. This command overrides the router or VRF command mode configuration. The default option removes this interface mode command and reverts to the router or VRF configuration, if present.
Configures the OSPFv2 priority, used to determine the DR for an area. The range is from 0 to 255. The
default is 1. See the “Designated Routers” section on page 5-3
.
Shuts down the OSPFv2 instance on this interface.
Example:
switch(config-if)# ip ospf shutdown
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Configuring Basic OSPFv2
This example shows how to add a network area 0.0.0.10 in OSPFv2 instance 201: switch# configure terminal switch(config)# interface ethernet 1/2 switch(config-if)# ip address 192.0.2.1/16 switch(config-if)# ip router ospf 201 area 0.0.0.10 switch(config-if)# copy running-config startup-config
Use the show ip ospf interface command to verify the interface configuration. Use the show ip ospf
neighbor command to see the neighbors for this interface.
Configuring Authentication for an Area
You can configure authentication for all networks in an area or for individual interfaces in the area.
Interface authentication configuration overrides area authentication.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the
“Enabling OSPFv2” section on page 5-15
).
Ensure that all neighbors on an interface share the same authentication configuration, including the shared authentication key.
Create the keychain for this authentication configuration. See the Cisco Nexus 9000 Series NX-OS
Security Configuration Guide.
Note
For OSPFv2, the key identifier in the key key-id command supports values from 0 to 255 only.
SUMMARY STEPS
1.
2.
3.
4.
5.
6.
7.
configure terminal
router ospf instance-tag
area area-id authentication [message-digest]
interface interface-type slot/port
(Optional) ip ospf authentication-key [0 | 3] key or
ip ospf message-digest-key key-id md5 [0 | 3] key
(Optional) show ip ospf instance-tag interface interface-type slot/port
(Optional) copy running-config startup-config
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DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 area
area-id authentication
[message-digest]
Purpose
Enters global configuration mode.
Creates a new OSPFv2 instance with the configured instance tag.
Configures the authentication mode for an area.
Example:
switch(config-router)# area 0.0.0.10 authentication
Step 4 interface
interface-type slot/port
Enters interface configuration mode.
Example:
switch(config-router)# interface ethernet 1/2 switch(config-if)#
Step 5 ip ospf authentication-key
[0 | 3] key
Example:
switch(config-if)# ip ospf authentication-key 0 mypass
(Optional) Configures simple password authentication for this interface. Use this command if the authentication is not set to keychain or message-digest.
0 configures the password in cleartext. 3 configures the password as 3DES encrypted.
ip ospf message-digest-key
key-id md5 [0
| 3] key
Example:
switch(config-if)# ip ospf message-digest-key 21 md5 0 mypass
(Optional) Configures message digest authentication for this interface. Use this command if the authentication is set to message-digest. The key-id range is from 1 to 255. The MD5 option 0 configures the password in cleartext and 3 configures the pass key as 3DES encrypted.
Step 6 show ip ospf
instance-tag interface
interface-type slot/port
(Optional) Displays OSPF information.
Example
: switch(config-if)# show ip ospf 201 interface ethernet 1/2
Step 7 copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
(Optional) Saves this configuration change.
Configuring Authentication for an Interface
You can configure authentication for individual interfaces in the area. Interface authentication configuration overrides area authentication.
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Configuring Basic OSPFv2
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the
“Enabling OSPFv2” section on page 5-15
).
Ensure that all neighbors on an interface share the same authentication configuration, including the shared authentication key.
Create the keychain for this authentication configuration. To configure OSPFv2 HMAC-SHA authentication, you must specify the HMAC-SHA algorithm to be used for the key. OSPFv2 will use the
MD5 cryptographic algorithm if cryptographic authentication using keychain is configured without selecting a cryptographic-algorithm. See the Cisco Nexus 9000 Series NX-OS Security Configuration
Guide.
Note
For OSPFv2, the key identifier in the key key-id command supports values from 0 to 255 only.
SUMMARY STEPS
6.
7.
4.
5.
8.
1.
2.
3.
configure terminal
interface interface-type slot/port
ip ospf authentication [message-digest]
(Optional) ip ospf authentication key-chain key-id
(Optional) ip ospf authentication-key [0 | 3 | 7] key
(Optional) ip ospf message-digest-key key-id md5 [0 | 3 | 7] key
(Optional) show ip ospf instance-tag interface interface-type slot/port
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 interface
interface-type slot/port
Example:
switch(config)# interface ethernet 1/2 switch(config-if)#
Step 3 ip ospf authentication
[message-digest]
Example:
switch(config-if)# ip ospf authentication
Step 4 ip ospf authentication key-chain
key-id
Example:
switch(config-if)# ip ospf authentication key-chain Test1
Purpose
Enters global configuration mode.
Enters interface configuration mode.
Enables interface authentication mode for OSPFv2 for either cleartext or message-digest type. Use this command to override area-based authentication for this interface. All neighbors must share this authentication type.
(Optional) Configures interface authentication to use keychains for OSPFv2. See the Cisco Nexus 9000
Series NX-OS Security Configuration Guide for details on keychains.
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Command
Step 5 ip ospf authentication-key
[0 | 3 | 7]
key
Example:
switch(config-if)# ip ospf authentication-key 0 mypass
Purpose
(Optional) Configures simple password authentication for this interface. Use this command if the authentication is not set to keychain or message-digest.
The options are as follows:
•
•
0—Configures the password in cleartext.
3—Configures the pass key as 3DES encrypted.
•
7—Configures the key as Cisco type 7 encrypted.
Step 6 ip ospf message-digest-key
key-id md5 [0
| 3 | 7] key
Example:
switch(config-if)# ip ospf message-digest-key 21 md5 0 mypass
(Optional) Configures message digest authentication for this interface. Use this command if the authentication is set to message-digest.The key-id range is from 1 to 255. The MD5 options are as follows:
•
0—Configures the password in cleartext.
Step 7 show ip ospf
instance-tag interface
interface-type slot/port
•
•
3—Configures the pass key as 3DES encrypted.
7—Configures the key as Cisco type 7 encrypted.
(Optional) Displays OSPF information.
Example
: switch(config-if)# show ip ospf 201 interface ethernet 1/2
Step 8 copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
(Optional) Saves this configuration change.
This example shows how to set an interface for simple, unencrypted passwords and set the password for
Ethernet interface 1/2: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# exit switch(config)# interface ethernet 1/2 switch(config-if)# ip router ospf 201 area 0.0.0.10 switch(config-if)# ip ospf authentication switch(config-if)# ip ospf authentication-key 0 mypass switch(config-if)# copy running-config startup-config
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Configuring Advanced OSPFv2
This example shows how to configure OSPFv2 HMAC-SHA-1 and MD5 cryptographic authentication: switch# configure terminal switch(config)# key chain chain1 switch(config-keychain)# key 1 switch(config-keychain-key)# key-string 7 070724404206 switch(config-keychain-key)# accept-lifetime 01:01:01 Jan 01 2015 infinite switch(config-keychain-key)# send-lifetime 01:01:01 Jan 01 2015 infinite switch(config-keychain-key)# cryptographic-algorithm HMAC-SHA-1 switch(config-keychain-key)# exit switch(config-keychain)# key 2 switch(config-keychain-key)# key-string 7 070e234f1f5b4a switch(config-keychain-key)# accept-lifetime 10:51:01 Jul 24 2015 infinite switch(config-keychain-key)# send-lifetime 10:51:01 Jul 24 2015 infinite switch(config-keychain-key)# cryptographic-algorithm MD5 switch(config-keychain-key)# exit switch(config-keychain)# exit switch(config)# interface ethernet 1/1 switch(config-if)# ip router ospf 1 area 0.0.0.0 switch(config-if)# ip ospf authentication message-digest switch(config-if)# ip ospf authentication key-chain chain1 switch(config-if)# show key chain chain1
Key-Chain chain1
Key 1 -- text 7 “070724404206”
cryptographic-algorithm HMAC-SHA-1
accept lifetime UTC (01:01:01 Jan 01 2015)-(always valid) [active]
send lifetime UTC (01:01:01 Jan 01 2015)-(always valid) [active]
Key 2 -- text 7 “070e234f1f5b4a”
cryptographic-algorithm MD5
accept lifetime UTC (10:51:00 Jul 24 2015)-(always valid) [active]
send lifetime UTC (10:51:00 Jul 24 2015)-(always valid) [active] switch(config-if)# show ip ospf interface ethernet 1/1
Ethernet1/1 is up, line protocol is up
IP address 11.11.11.1/24
Process ID 1 VRF default, area 0.0.0.3
Enabled by interface configuration
State BDR, Network type BROADCAST, cost 40
Index 6, Transmit delay 1 sec, Router Priority 1
Designated Router ID: 33.33.33.33, address: 11.11.11.3
Backup Designated Router ID: 1.1.1.1, address: 11.11.11.1
2 Neighbors, flooding to 2, adjacent with 2
Timer intervals: Hello 10, Dead 40, Wait 40, Retransmit 5
Hello timer due in 00:00:08
Message-digest authentication, using keychain key1 (ready)
Sending SA: Key id 2, Algorithm MD5
Number of opaque link LSAs: 0, checksum sum 0
Configuring Advanced OSPFv2
Configure OSPFv2 after you have designed your OSPFv2 network.
This section includes the following topics:
•
•
•
•
Configuring Filter Lists for Border Routers, page 5-25
Configuring Stub Areas, page 5-26
Configuring a Totally Stubby Area, page 5-27
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•
•
•
•
•
•
•
•
•
•
Configuring Multi-Area Adjacency, page 5-30
Configuring Virtual Links, page 5-31
Configuring Redistribution, page 5-33
Limiting the Number of Redistributed Routes, page 5-35
Configuring Route Summarization, page 5-37
Configuring Stub Route Advertisements, page 5-38
Configuring the Administrative Distance of Routes, page 5-39
Modifying the Default Timers, page 5-42
Configuring Graceful Restart, page 5-44
Restarting an OSPFv2 Instance, page 5-46
Configuring Filter Lists for Border Routers
You can separate your OSPFv2 domain into a series of areas that contain related networks. All areas must connect to the backbone area through an area border router (ABR). OSPFv2 domains can connect to external domains through an autonomous system border router (ASBR). See the
.
ABRs have the following optional configuration parameters:
•
Area range—Configures route summarization between areas. See the
Summarization” section on page 5-37 .
•
Filter list—Filters the Network Summary (type 3) LSAs that are allowed in from an external area.
ASBRs also support filter lists.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the
“Enabling OSPFv2” section on page 5-15 ).
Create the route map that the filter list uses to filter IP prefixes in incoming or outgoing Network
Summary (type 3) LSAs. See Chapter 15, “Configuring Route Policy Manager.”
SUMMARY STEPS
3.
4.
1.
2.
5.
configure terminal
router ospf instance-tag
area area-id filter-list route-map map-name {in | out}
(Optional) show ip ospf policy statistics area id filter-list {in | out}
(Optional) copy running-config startup-config
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DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 area
area-id filter-list route-map
map-name {in | out}
Example:
switch(config-router)# area 0.0.0.10 filter-list route-map FilterLSAs in
Step 4 show ip ospf policy statistics area
id
filter-list
{in | out}
Example
: switch(config-if)# show ip ospf policy statistics area 0.0.0.10 filter-list in
Step 5 copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
Purpose
Enters global configuration mode.
Creates a new OSPFv2 instance with the configured instance tag.
Filters incoming or outgoing Network Summary (type
3) LSAs on an ABR.
(Optional) Displays OSPF policy information.
(Optional) Saves this configuration change.
This example shows how to configure a filter list in area 0.0.0.10: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# area 0.0.0.10 filter-list route-map FilterLSAs in switch(config-router)# copy running-config startup-config
Configuring Stub Areas
You can configure a stub area for part of an OSPFv2 domain where external traffic is not necessary. Stub areas block AS External (type 5) LSAs and limit unnecessary routing to and from selected networks. See the
“Stub Area” section on page 5-9
. You can optionally block all summary routes from going into the stub area.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the
“Enabling OSPFv2” section on page 5-15
).
Ensure that there are no virtual links or ASBRs in the proposed stub area.
SUMMARY STEPS
1.
configure terminal
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4.
5.
2.
3.
6.
router ospf instance-tag
area area-id stub
(Optional) area area-id default-cost cost
(Optional) show ip ospf instance-tag
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 area
area-id stub
Example:
switch(config-router)# area 0.0.0.10 stub
Step 4 area
area-id default-cost cost
Example:
switch(config-router)# area 0.0.0.10 default-cost 25
Step 5 show ip ospf
instance-tag
Example
: switch(config-if)# show ip ospf 201
Step 6 copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
Purpose
Enters global configuration mode.
Creates a new OSPFv2 instance with the configured instance tag.
Creates this area as a stub area.
(Optional) Sets the cost metric for the default summary route sent into this stub area. The range is from 0 to
16777215. The default is 1.
(Optional) Displays OSPF information.
(Optional) Saves this configuration change.
This example shows how to create a stub area: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# area 0.0.0.10 stub switch(config-router)# copy running-config startup-config
Configuring a Totally Stubby Area
You can create a totally stubby area and prevent all summary route updates from going into the stub area.
To create a totally stubby area, use the following command in router configuration mode:
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Command area
area-id stub no-summary
Example:
switch(config-router)# area 20 stub no-summary
Purpose
Creates this area as a totally stubby area.
Configuring NSSA
You can configure an NSSA for part of an OSPFv2 domain where limited external traffic is required. For
information about NSSAs, see the “Not-So-Stubby Area” section on page 5-9
. You can optionally translate this external traffic to an AS External (type 5) LSA and flood the OSPFv2 domain with this routing information. An NSSA can be configured with the following optional parameters:
•
No redistribution—Redistributed routes bypass the NSSA and are redistributed to other areas in the
OSPFv2 autonomous system. Use this option when the NSSA ASBR is also an ABR.
•
•
Default information originate—Generates an NSSA External (type 7) LSA for a default route to the external autonomous system. Use this option on an NSSA ASBR if the ASBR contains the default route in the routing table. This option can be used on an NSSA ABR whether or not the ABR contains the default route in the routing table.
Route map—Filters the external routes so that only those routes that you want are flooded throughout the NSSA and other areas.
•
•
Translate—Translates NSSA External LSAs to AS External LSAs for areas outside the NSSA. Use this command on an NSSA ABR to flood the redistributed routes throughout the OSPFv2 autonomous system. You can optionally suppress the forwarding address in these AS External LSAs.
If you choose this option, the forwarding address is set to 0.0.0.0.
No summary—Blocks all summary routes from flooding the NSSA. Use this option on the NSSA
ABR.
BEFORE YOU BEGIN
Ensure that you have enabled the OSPF feature (see the
“Enabling OSPFv2” section on page 5-15
).
Ensure that there are no virtual links in the proposed NSSA and that it is not the backbone area.
SUMMARY STEPS
4.
5.
6.
1.
2.
3.
configure terminal
router ospf instance-tag
area area-id nssa [no-redistribution] [default-information-originate [route-map map-name]]
[no-summary] [translate type7 {always | never} [suppress-fa]]
(Optional) area area-id default-cost cost
(Optional) show ip ospf instance-tag
(Optional) copy running-config startup-config
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DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 area
area-id nssa [no-redistribution]
[default-information-originate
[route-map map-name]] [no-summary]
[translate type7 {always | never}
[suppress-fa]]
Example:
switch(config-router)# area 0.0.0.10 nssa
Step 4 area
area-id default-cost cost
Example:
switch(config-router)# area 0.0.0.10 default-cost 25
Step 5 show ip ospf
instance-tag
Example
: switch(config-if)# show ip ospf 201
Step 6 copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
Purpose
Enters global configuration mode.
Creates a new OSPFv2 instance with the configured instance tag.
Creates this area as an NSSA.
(Optional) Sets the cost metric for the default summary route sent into this NSSA.
(Optional) Displays OSPF information.
(Optional) Saves this configuration change.
This example shows how to create an NSSA that blocks all summary route updates: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# area 0.0.0.10 nssa no-summary switch(config-router)# copy running-config startup-config
This example shows how to create an NSSA that generates a default route: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# area 0.0.0.10 nssa default-info-originate switch(config-router)# copy running-config startup-config
This example shows how to create an NSSA that filters external routes and blocks all summary route updates: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# area 0.0.0.10 nssa route-map ExternalFilter no-summary switch(config-router)# copy running-config startup-config
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This example shows how to create an NSSA that always translates NSSA External (type 5) LSAs to AS
External (type 7) LSAs: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# area 0.0.0.10 nssa translate type 7 always switch(config-router)# copy running-config startup-config
Configuring Multi-Area Adjacency
You can add more than one area to an existing OSPFv2 interface. The additional logical interfaces support multi-area adjacency.
BEFORE YOU BEGIN
You must enable OSPFv2 (see the
“Enabling OSPFv2” section on page 5-15 ).
Ensure that you have configured a primary area for the interface (see the
OSPFv2” section on page 5-18 ).
SUMMARY STEPS
3.
4.
1.
2.
5.
configure terminal
interface interface-type slot/port
ip router ospf [instance-tag] multi-area area-id
(Optional) show ip ospf instance-tag interface interface-type slot/port
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Purpose
Enters global configuration mode.
Example:
switch# configure terminal switch(config)#
Step 2 interface
interface-type slot/port
Enters interface configuration mode.
Example:
switch(config)# interface ethernet 1/2 switch(config-if)#
Step 3 ip router ospf
[instance-tag] multi-area
area-id
Example:
switch(config-if)# ip router ospf 201 multi-area 3
Adds the interface to another area.
Note
Beginning with Cisco NX-OS Release
7.0(3)I5(1), the instance-tag argument is optional. If you do not specify an instance, the multi-area configuration is applied to the same instance that is configured for the primary area on that interface.
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Command
Step 4 show ip ospf
instance-tag interface
interface-type slot/port
Example
: switch(config-if)# show ip ospf 201 interface ethernet 1/2
Step 5 copy running-config startup-config
Example:
switch(config)# copy running-config startup-config
Purpose
(Optional) Displays OSPFv2 information.
(Optional) Saves this configuration change.
This example shows how to add a second area to an OSPFv2 interface: switch# configure terminal switch(config)# interface ethernet 1/2 switch(config-if)# ip address 192.0.2.1/16 switch(config-if)# ip router ospf 201 area 0.0.0.10 switch(config-if)# ip router ospf 201 multi-area 20 switch(config-if)# copy running-config startup-config
Configuring Virtual Links
A virtual link connects an isolated area to the backbone area through an intermediate area. See the
“Virtual Links” section on page 5-10
. You can configure the following optional parameters for a virtual link:
•
•
Authentication—Sets a simple password or MD5 message digest authentication and associated keys.
Dead interval—Sets the time that a neighbor waits for a Hello packet before declaring the local router as dead and tearing down adjacencies.
•
•
•
Hello interval—Sets the time between successive Hello packets.
Retransmit interval—Sets the estimated time between successive LSAs.
Transmit delay—Sets the estimated time to transmit an LSA to a neighbor.
Note
You must configure the virtual link on both routers involved before the link becomes active.
You cannot add a virtual link to a stub area.
BEFORE YOU BEGIN
Ensure that you have enabled OSPF (see the
“Enabling OSPFv2” section on page 5-15 ).
SUMMARY STEPS
1.
2.
3.
4.
5.
configure terminal
router ospf instance-tag
area area-id virtual-link router-id
(Optional) show ip ospf virtual-link [brief]
(Optional) copy running-config startup-config
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DETAILED STEPS
Command
Step 1 configure terminal
Purpose
Enters global configuration mode.
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Creates a new OSPFv2 instance with the configured instance tag.
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 area
area-id virtual-link router-id
Example:
switch(config-router)# area 0.0.0.10 virtual-link 10.1.2.3
switch(config-router-vlink)#
Step 4 show ip ospf virtual-link
[brief]
Creates one end of a virtual link to a remote router.
You must create the virtual link on that remote router to complete the link.
(Optional) Displays OSPF virtual link information.
Example
: switch(config-router-vlink)# show ip ospf virtual-link
Step 5 copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router-vlink)# copy running-config startup-config
You can configure the following optional commands in virtual link configuration mode:
Command authentication
[key-chain key-id |
message-digest
| null]
Example:
switch(config-router-vlink)# authentication message-digest
authentication-key
[0 | 3] key
Example:
switch(config-router-vlink)# authentication-key 0 mypass
dead-interval
seconds
Example
: switch(config-router-vlink)# dead-interval 50
hello-interval
seconds
Example:
switch(config-router-vlink)# hello-interval 25
Purpose
(Optional) Overrides area-based authentication for this virtual link.
(Optional) Configures a simple password for this virtual link. Use this command if the authentication is not set to keychain or message-digest. 0 configures the password in cleartext. 3 configures the password as 3DES encrypted.
(Optional) Configures the OSPFv2 dead interval, in seconds. The range is from 1 to 65535. The default is four times the hello interval, in seconds.
(Optional) Configures the OSPFv2 hello interval, in seconds. The range is from 1 to 65535. The default is 10 seconds.
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Command Purpose message-digest-key
key-id md5 [0 | 3]
key
Example:
switch(config-router-vlink)# message-digest-key 21 md5 0 mypass
(Optional) Configures message digest authentication for this virtual link. Use this command if the authentication is set to message-digest. 0 configures the password in cleartext. 3 configures the pass key as 3DES encrypted.
retransmit-interval
seconds
(Optional) Configures the OSPFv2 retransmit interval, in seconds. The range is from 1 to 65535. The default is 5.
Example
: switch(config-router-vlink)# retransmit-interval 50
transmit-delay
seconds
(Optional) Configures the OSPFv2 transmit-delay, in seconds. The range is from 1 to 450. The default is 1.
Example:
switch(config-router-vlink)# transmit-delay 2
This example shows how to create a simple virtual link between two ABRs.
The configuration for ABR 1 (router ID 27.0.0.55) is as follows: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# area 0.0.0.10 virtual-link 10.1.2.3 switch(config-router)# copy running-config startup-config
The configuration for ABR 2 (Router ID 10.1.2.3) is as follows: switch# configure terminal switch(config)# router ospf 101 switch(config-router)# area 0.0.0.10 virtual-link 27.0.0.55 switch(config-router)# copy running-config startup-config
Configuring Redistribution
You can redistribute routes learned from other routing protocols into an OSPFv2 autonomous system through the ASBR.
You can configure the following optional parameters for route redistribution in OSPF:
•
Default information originate—Generates an AS External (type 5) LSA for a default route to the external autonomous system.
Note
Default information originate ignores match statements in the optional route map.
•
Default metric—Sets all redistributed routes to the same cost metric.
Note
If you redistribute static routes, Cisco NX-OS also redistributes the default static route.
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BEFORE YOU BEGIN
Ensure that you have enabled OSPF (see the
“Enabling OSPFv2” section on page 5-15
).
Create the necessary route maps used for redistribution.
SUMMARY STEPS
3.
4.
1.
2.
5.
6.
configure terminal
router ospf instance-tag
redistribute {bgp id | direct | eigrp id | isis id | ospf id | rip id | static} route-map map-name
default-information originate [always] [route-map map-name]
default-metric cost
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Purpose
Enters global configuration mode.
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Example:
switch(config-router)# default-information-originate route-map
DefaultRouteFilter
Creates a new OSPFv2 instance with the configured instance tag.
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 redistribute
{bgp id | direct | eigrp id
| isis id | ospf id | rip id | static}
route-map
map-name
Redistributes the selected protocol into OSPF through the configured route map.
Example:
switch(config-router)# redistribute bgp route-map FilterExternalBGP
Note
If you redistribute static routes, Cisco NX-OS also redistributes the default static route.
Step 4 default-information originate
[always]
[route-map map-name]
Creates a default route into this OSPF domain if the default route exists in the RIB. Use the following optional keywords:
•
always —Always generates the default route of
0.0.0. even if the route does not exist in the RIB.
•
Note
route-map—Generates the default route if the route map returns true.
This command ignores match statements in the route map.
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Command
Step 5 default-metric
cost
Example:
switch(config-router)# default-metric 25
Step 6 copy running-config startup-config
Purpose
Sets the cost metric for the redistributed routes. This command does not apply to directly connected routes.
Use a route map to set the default metric for directly connected routes.
Note
If you do not specify a metric, OSPF uses a default value of 20 when redistributing routes from all protocols except Border Gateway
Protocol (BGP) routes, which use a metric of 1.
(Optional) Saves this configuration change.
Example:
switch(config-router)# copy running-config startup-config
This example shows how to redistribute the Border Gateway Protocol (BGP) into OSPF: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# redistribute bgp route-map FilterExternalBGP switch(config-router)# copy running-config startup-config
Limiting the Number of Redistributed Routes
Route redistribution can add many routes to the OSPFv2 route table. You can configure a maximum limit to the number of routes accepted from external protocols. OSPFv2 provides the following options to configure redistributed route limits:
•
Fixed limit—Logs a message when OSPFv2 reaches the configured maximum. OSPFv2 does not accept any more redistributed routes. You can optionally configure a threshold percentage of the maximum where OSPFv2 logs a warning when that threshold is passed.
•
•
Warning only—Logs a warning only when OSPFv2 reaches the maximum. OSPFv2 continues to accept redistributed routes.
Withdraw—Starts the timeout period when OSPFv2 reaches the maximum. After the timeout period,
OSPFv2 requests all redistributed routes if the current number of redistributed routes is less than the maximum limit. If the current number of redistributed routes is at the maximum limit, OSPFv2 withdraws all redistributed routes. You must clear this condition before OSPFv2 accepts more redistributed routes.
•
You can optionally configure the timeout period.
BEFORE YOU BEGIN
Ensure that you have enabled OSPF (see the
“Enabling OSPFv2” section on page 5-15 ).
SUMMARY STEPS
1.
2.
3.
4.
configure terminal
router ospf instance-tag
redistribute {bgp id | direct | eigrp id | isis id | ospf id | rip id | static} route-map map-name
redistribute maximum-prefix max [threshold] [warning-only | withdraw [num-retries timeout]]
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5.
6.
(Optional) show running-config ospf
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Purpose
Enters global configuration mode.
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Creates a new OSPFv2 instance with the configured instance tag.
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 redistribute
{bgp id | direct | eigrp id
| isis id | ospf id | rip id | static}
route-map
map-name
Redistributes the selected protocol into OSPF through the configured route map.
Example:
switch(config-router)# redistribute bgp route-map FilterExternalBGP
Step 4 redistribute maximum-prefix
max
[threshold] [warning-only | withdraw
[num-retries timeout]]
Example:
switch(config-router)# redistribute maximum-prefix 1000 75 warning-only
Step 5 show running-config ospf
Specifies a maximum number of prefixes that OSPFv2 distributes. The range is from 1 to 65535. Optionally specifies the following:
•
threshold—Percentage of maximum prefixes that trigger a warning message.
•
•
warning-only—Logs a warning message when the maximum number of prefixes is exceeded.
withdraw—Withdraws all redistributed routes.
Optionally tries to retrieve the redistributed routes. The num-retries range is from 1 to 12. The
timeout is 60 to 600 seconds. The default is 300 seconds. Use the clear ip ospf redistribution command if all routes are withdrawn.
(Optional) Displays the OSPFv2 configuration.
Example:
switch(config-router)# show running-config ospf
Step 6 copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config-router)# copy running-config startup-config
This example shows how to limit the number of redistributed routes into OSPF: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# redistribute bgp route-map FilterExternalBGP switch(config-router)# redistribute maximum-prefix 1000 75
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Configuring Route Summarization
You can configure route summarization for inter-area routes by configuring an address range that is summarized. You can also configure route summarization for external, redistributed routes by configuring a summary address for those routes on an ASBR. For more information, see the
Summarization” section on page 5-10 .
BEFORE YOU BEGIN
Ensure that you have enabled OSPF (see the
“Enabling OSPFv2” section on page 5-15 ).
SUMMARY STEPS
4.
5.
6.
1.
2.
3.
configure terminal
router ospf instance-tag
area area-id range ip-prefix/length [no-advertise] [cost cost] or
summary-address ip-prefix/length [no-advertise | tag tag-id]
(Optional) show ip ospf summary-address
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 area
area-id range ip-prefix/length
[no-advertise] [cost cost]
Purpose
Enters global configuration mode.
Creates a new OSPFv2 instance with the configured instance tag.
Example:
switch(config-router)# area 0.0.0.10 range 10.3.0.0/16
Step 4 summary-address
ip-prefix/length
[no-advertise | tag tag]
Example:
switch(config-router)# summary-address
10.5.0.0/16 tag 2
Creates a summary address on an ABR for a range of addresses and optionally does not advertise this summary address in a Network Summary (type 3)
LSA. The cost range is from 0 to 16777215.
Creates a summary address on an ASBR for a range of addresses and optionally assigns a tag for this summary address that can be used for redistribution with route maps.
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Command
Step 5 show ip ospf summary-address
Example
: switch(config-router)# show ip ospf summary-address
Step 6 copy running-config startup-config
Example:
switch(config-router)# copy running-config startup-config
Purpose
(Optional) Displays information about OSPF summary addresses.
(Optional) Saves this configuration change.
This example shows how to create summary addresses between areas on an ABR: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# area 0.0.0.10 range 10.3.0.0/16 switch(config-router)# copy running-config startup-config
This example shows how to create summary addresses on an ASBR: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# summary-address 10.5.0.0/16 switch(config-router)# no discard-route internal switch(config-router)# copy running-config startup-config
Configuring Stub Route Advertisements
Use stub route advertisements when you want to limit the OSPFv2 traffic through this router for a short
time. For more information, see the “OSPFv2 Stub Router Advertisements” section on page 5-12
.
Stub route advertisements can be configured with the following optional parameters:
•
•
On startup—Sends stub route advertisements for the specified announce time.
Wait for BGP—Sends stub router advertisements until BGP converges.
Note
You should not save the running configuration of a router when it is configured for a graceful shutdown because the router continues to advertise a maximum metric after it is reloaded.
BEFORE YOU BEGIN
Ensure that you have enabled OSPF (see the
“Enabling OSPFv2” section on page 5-15
).
SUMMARY STEPS
1.
2.
3.
4.
configure terminal
router ospf instance-tag
max-metric router-lsa [external-lsa [max-metric-value]] [include-stub] [on-startup {seconds |
wait-for bgp tag}] [summary-lsa [max-metric-value]]
(Optional) copy running-config startup-config
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DETAILED STEPS
Command
Step 1 configure terminal
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 max-metric router-lsa
[external-lsa
[max-metric-value]] [include-stub]
[on-startup {seconds | wait-for bgp
tag}] [summary-lsa [max-metric-value]]
Example:
switch(config-router)# max-metric router-lsa
Step 4 copy running-config startup-config
Example:
switch(config-router)# copy running-config startup-config
Purpose
Enters global configuration mode.
Creates a new OSPFv2 instance with the configured instance tag.
Configures OSPFv2 stub route advertisements.
(Optional) Saves this configuration change.
This example shows how to enable the stub router advertisements on startup for the default 600 seconds: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# max-metric router-lsa on-startup switch(config-router)# copy running-config startup-config
Configuring the Administrative Distance of Routes
You can set the administrative distance of routes added by OSPFv2 into the RIB.
The administrative distance is a rating of the trustworthiness of a routing information source. A higher value indicates a lower trust rating. Typically, a route can be learned through more than one routing protocol. The administrative distance is used to discriminate between routes learned from more than one routing protocol. The route with the lowest administrative distance is installed in the IP routing table.
BEFORE YOU BEGIN
Ensure that you have enabled OSPF (see the
“Enabling OSPFv2” section on page 5-15 ).
SUMMARY STEPS
1.
2.
configure terminal
router ospf instance-tag
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9.
10.
7.
8.
5.
6.
3.
4.
[no] table-map map-name
exit
route-map map-name [permit | deny] [seq]
match route-type route-type
match ip route-source prefix-list name
match ip address prefix-list name
set distance value
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Purpose
Enters global configuration mode.
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Creates a new OSPFv2 instance with the configured instance tag.
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3
[no] table-map map-name
Example:
switch(config-router)# table-map foo
Step 4 exit
Configures the policy for filtering or modifying
OSPFv2 routes before sending them to the RIB. You can enter up to 63 alphanumeric characters for the map name.
Exits router configuration mode.
Example:
switch(config-router)# exit switch(config)#
Step 5 route-map
map-name [permit | deny] [seq]
Example:
switch(config)# route-map foo permit 10 switch(config-route-map)#
Creates a route map or enters route-map configuration mode for an existing route map. Use seq to order the entries in a route map.
Note
The permit option enables you to set the distance. If you use the deny option, the default distance is applied.
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Configuring Advanced OSPFv2
Command
Step 6 match route-type
route-type
Example:
switch(config-route-map)# match route-type external
Step 7 match ip route-source prefix-list
name
Example:
switch(config-route-map)# match ip route-source prefix-list p1
Step 8 match ip address prefix-list
name
Example:
switch(config-route-map)# match ip address prefix-list p1
Step 9 set distance
value
Example:
switch(config-route-map)# set distance
150
Step 10 copy running-config startup-config
Example:
switch(config-route-map)# copy running-config startup-config
Purpose
Matches against one of the following route types:
•
external—The external route (BGP, EIGRP, and
OSPF type 1 or 2)
•
•
•
•
inter-area—OSPF inter-area route internal—The internal route (including the OSPF intra- or inter-area) intra-area—OSPF intra-area route nssa-external—The NSSA external route (OSPF type 1 or 2).
•
•
type-1—The OSPF external type 1 route type-2—The OSPF external type 2 route
Matches the IPv4 route source address or router ID of a route to one or more IP prefix lists. Use the ip
prefix-list command to create the prefix list.
Matches against one or more IPv4 prefix lists. Use the
ip prefix-list command to create the prefix list.
Sets the administrative distance of routes for OSPFv2.
The range is from 1 to 255.
(Optional) Saves this configuration change.
This example shows how to configure the OSPFv2 administrative distance for inter-area routes to 150, for external routes to 200, and for all prefixes in prefix list p1 to 190: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# table-map foo switch(config-router)# exit switch(config)# route-map foo permit 10 switch(config-route-map)# match route-type inter-area switch(config-route-map)# set distance 150 switch(config)# route-map foo permit 20 switch(config-route-map)# match route-type external switch(config-route-map)# set distance 200 switch(config)# route-map foo permit 30 switch(config-route-map)# match ip route-source prefix-list p1 switch(config-route-map)# match ip address prefix-list p1 switch(config-route-map)# set distance 190
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Configuring Advanced OSPFv2
Modifying the Default Timers
OSPFv2 includes a number of timers that control the behavior of protocol messages and shortest path first (SPF) calculations. OSPFv2 includes the following optional timer parameters:
•
LSA arrival time—Sets the minimum interval allowed between LSAs that arrive from a neighbor.
LSAs that arrive faster than this time are dropped.
•
•
Pacing LSAs—Sets the interval at which LSAs are collected into a group and refreshed, checksummed, or aged. This timer controls how frequently LSA updates occur and optimizes how many are sent in an LSA update message (see the
“Flooding and LSA Group Pacing” section on page 5-6 ).
Throttle LSAs—Sets the rate limits for generating LSAs. This timer controls how frequently LSAs are generated after a topology change occurs.
•
Throttle SPF calculation—Controls how frequently the SPF calculation is run.
At the interface level, you can also control the following timers:
•
•
Retransmit interval—Sets the estimated time between successive LSAs.
Transmit delay—Sets the estimated time to transmit an LSA to a neighbor.
See the
“Configuring Networks in OSPFv2” section on page 5-18 for information about the hello
interval and dead timer.
BEFORE YOU BEGIN
Ensure that you have enabled OSPF (see the
“Enabling OSPFv2” section on page 5-15
).
SUMMARY STEPS
1.
2.
configure terminal
router ospf instance-tag
timers lsa-arrival msec
5.
6.
3.
4.
timers lsa-group-pacing seconds
timers throttle lsa start-time hold-interval max-time
timers throttle spf delay-time hold-time
interface type slot/port
9.
10.
7.
8.
ip ospf hello-interval seconds
ip ospf dead-interval seconds
ip ospf retransmit-interval seconds
ip ospf transmit-delay seconds
11.
12.
13.
(Optional) show ip ospf
(Optional) copy running-config startup-config
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Configuring Advanced OSPFv2
DETAILED STEPS
Command
Step 1 configure terminal
Purpose
Enters global configuration mode.
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Creates a new OSPFv2 instance with the configured instance tag.
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 timers lsa-arrival
msec
Sets the LSA arrival time in milliseconds. The range is from 10 to 600000. The default is 1000 milliseconds.
Example:
switch(config-router)# timers lsa-arrival 2000
Step 4 timers lsa-group-pacing
seconds
Sets the interval in seconds for grouping LSAs. The range is from 1 to 1800. The default is 10 seconds.
Example:
switch(config-router)# timers lsa-group-pacing 200
Step 5 timers throttle lsa
start-time
hold-interval max-time
Example:
switch(config-router)# timers throttle lsa 3000
Sets the rate limit in milliseconds for generating LSAs with the following timers:
start-time—The range is from 0 to 5000 milliseconds.
The default value is 0 milliseconds.
hold-interval—The range is from 50 to 30,000 milliseconds. The default value is 5000 milliseconds.
Step 6 timers throttle spf
delay-time hold-time
max-wait
Example:
switch(config-router)# timers throttle spf 3000 2000 4000
max-time—The range is from 50 to 30,000 milliseconds. The default value is 5000 milliseconds.
Sets the SPF best-path schedule initial delay time and the minimum hold time in seconds between SPF best-path calculations. The range is from 1 to 600000.
The default is no delay time and a 5000-millisecond hold time.
Step 7 interface
type slot/port
Enters interface configuration mode.
Example
: switch(config)# interface ethernet 1/2 switch(config-if)#
Step 8 ip ospf hello-interval
seconds
Sets the hello interval for this interface. The range is from 1 to 65535. The default is 10.
Example:
switch(config-if)# ip ospf hello-interval 30
Step 9 ip ospf dead-interval
seconds
Example:
switch(config-if)# ip ospf dead-interval
30
Sets the dead interval for this interface. The range is from 1 to 65535.
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Command
Step 10 ip ospf retransmit-interval
seconds
Example:
switch(config-if)# ip ospf retransmit-interval 30
Step 11 ip ospf transmit-delay
seconds
Example:
switch(config-if)# ip ospf transmit-delay 600 switch(config-if)#
Step 12 show ip ospf
Example
: switch(config-if)# show ip ospf
Step 13 copy running-config startup-config
Example:
switch(config-if)# copy running-config startup-config
Purpose
Sets the estimated time in seconds between LSAs transmitted from this interface. The range is from 1 to
65535. The default is 5.
Sets the estimated time in seconds to transmit an LSA to a neighbor. The range is from 1 to 450. The default is 1.
(Optional) Displays information about OSPF.
(Optional) Saves this configuration change.
This example shows how to control LSA flooding with the lsa-group-pacing option: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# timers lsa-group-pacing 300 switch(config-router)# copy running-config startup-config
Configuring Graceful Restart
Graceful restart is enabled by default. You can configure the following optional parameters for graceful restart in an OSPFv2 instance:
•
Grace period—Configures how long neighbors should wait after a graceful restart has started before tearing down adjacencies.
•
•
Helper mode disabled—Disables helper mode on the local OSPFv2 instance. OSPFv2 does not participate in the graceful restart of a neighbor.
Planned graceful restart only—Configures OSPFv2 to support graceful restart only in the event of a planned restart.
BEFORE YOU BEGIN
Ensure that you have enabled OSPF (see the
“Enabling OSPFv2” section on page 5-15
).
Ensure that all neighbors are configured for graceful restart with matching optional parameters set.
SUMMARY STEPS
3.
4.
1.
2.
configure terminal
router ospf instance-tag
graceful-restart
(Optional) graceful-restart grace-period seconds
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7.
8.
5.
6.
(Optional) graceful-restart helper-disable
(Optional) graceful-restart planned-only
(Optional) show ip ospf instance-tag
(Optional) copy running-config startup-config
DETAILED STEPS
Command
Step 1 configure terminal
Purpose
Enters global configuration mode.
Example:
switch# configure terminal switch(config)#
Step 2 router ospf
instance-tag
Creates a new OSPFv2 instance with the configured instance tag.
Example:
switch(config)# router ospf 201 switch(config-router)#
Step 3 graceful-restart
Example:
switch(config-router)# graceful-restart
Step 4 graceful-restart grace-period
seconds
Example:
switch(config-router)# graceful-restart helper-disable
Step 6 graceful-restart planned-only
Enables a graceful restart. A graceful restart is enabled by default.
Example:
switch(config-router)# graceful-restart grace-period 120
Step 5 graceful-restart helper-disable
(Optional) Sets the grace period, in seconds. The range is from 5 to 1800. The default is 60 seconds.
(Optional) Disables helper mode. This feature is enabled by default.
(Optional) Configures a graceful restart for planned restarts only.
Example:
switch(config-router)# graceful-restart planned-only
Step 7 show ip ospf
instance-tag
(Optional) Displays OSPF information.
Example
: switch(config-if)# show ip ospf 201
Step 8 copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config startup-config
This example shows how to enable a graceful restart if it has been disabled and set the grace period to
120 seconds: switch# configure terminal switch(config)# router ospf 201 switch(config-router)# graceful-restart switch(config-router)# graceful-restart grace-period 120 switch(config-router)# copy running-config startup-config
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Configuring Advanced OSPFv2
Restarting an OSPFv2 Instance
You can restart an OSPv2 instance. This action clears all neighbors for the instance.
To restart an OSPFv2 instance and remove all associated neighbors, use the following command:
Command restart ospf
instance-tag
Example:
switch(config)# restart ospf 201
Purpose
Restarts the OSPFv2 instance and removes all neighbors.
Configuring OSPFv2 with Virtualization
You can configure multiple OSPFv2 instances. You can also create multiple VRFs and use the same or multiple OSPFv2 instances in each VRF. You assign an OSPFv2 interface to a VRF.
Note
Configure all other parameters for an interface after you configure the VRF for an interface. Configuring a VRF for an interface deletes all the configuration for that interface.
BEFORE YOU BEGIN
Ensure that you have enabled OSPF (see the
“Enabling OSPFv2” section on page 5-15
).
SUMMARY STEPS
1.
2.
3.
4.
configure terminal
vrf context vrf_name
router ospf instance-tag
vrf vrf-name
9.
10.
7.
8.
5.
6.
(Optional) maximum-paths paths
interface interface-type slot/port
vrf member vrf-name
ip-address ip-prefix/length
router ospf instance-tag area area-id
(Optional) copy running-config startup-config
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DETAILED STEPS
Command
Step 1 configure terminal
Purpose
Enters global configuration mode.
Example:
switch# configure terminal switch(config)#
Step 2 vrf context
vrf-name
Creates a new VRF and enters VRF configuration mode.
Example:
switch(config)# vrf context
RemoteOfficeVRF switch(config-vrf)#
Step 3 router ospf
instance-tag
Creates a new OSPFv2 instance with the configured instance tag.
Example:
switch(config-vrf)# router ospf 201 switch(config-router)#
Step 4 vrf
vrf-name
Enters VRF configuration mode.
Example:
switch(config-router)# vrf
RemoteOfficeVRF switch(config-router-vrf)#
Step 5 maximum-paths
paths
Example
: switch(config-router-vrf)# maximum-paths
4
(Optional) Configures the maximum number of equal
OSPFv2 paths to a destination in the route table for this
VRF. This feature is used for load balancing.
Step 6 interface
interface-type slot/port
Enters interface configuration mode.
Example
: switch(config-router-vrf)# interface ethernet 1/2 switch(config-if)#
Step 7 vrf member
vrf-name
Adds this interface to a VRF.
Example:
switch(config-if)# vrf member
RemoteOfficeVRF
Step 8 ip address
ip-prefix/length
Example:
switch(config-if)# ip address
192.0.2.1/16
Step 9 ip router ospf
instance-tag area area-id
Configures an IP address for this interface. You must do this step after you assign this interface to a VRF.
Assigns this interface to the OSPFv2 instance and area configured.
Example:
switch(config-if)# ip router ospf 201 area 0
Step 10 copy running-config startup-config
(Optional) Saves this configuration change.
Example:
switch(config)# copy running-config startup-config
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Verifying the OSPFv2 Configuration
This example shows how to create a VRF and add an interface to the VRF: switch# configure terminal switch(config)# vrf context NewVRF switch(config)# router ospf 201 switch(config)# interface ethernet 1/2 switch(config-if)# vrf member NewVRF switch(config-if)# ip address 192.0.2.1/16 switch(config-if)# ip router ospf 201 area 0 switch(config)# copy running-config startup-config
Verifying the OSPFv2 Configuration
To display the OSPFv2 configuration, perform one of the following tasks:
Command Purpose
show ip ospf [instance-tag] [vrf vrf-name] Displays information about one or more OSPF routing instances. The output includes the following area-level counts:
•
•
Interfaces in this area—A count of all interfaces added to this area (configured interfaces).
Active interfaces—A count of all interfaces considered to be in router link states and SPF (UP interfaces).
•
Passive interfaces—A count of all interfaces considered to be OSPF passive (no adjacencies will be formed).
•
Loopback interfaces—A count of all local loopback interfaces.
Displays the OSPFv2 border router configuration.
show ip ospf border-routers
[vrf
{vrf-name | all | default | management}]
show ip ospf database
[vrf {vrf-name | all
| default | management}]
Displays the OSPFv2 link-state database summary.
Displays OSPFv2-related interface information.
show ip ospf interface number [vrf
{vrf-name | all | default | management}]
show ip ospf lsa-content-changed-list
neighbor-id interface
-
type number
[vrf
{vrf-name | all | default | management}]
Displays the OSPFv2 LSAs that have changed.
show ip ospf neighbors [neighbor-id]
[detail] [interface
-
type number] [vrf
{vrf-name | all | default | management}]
[summary]
show ip ospf request-list
neighbor-id interface
-
type number
[vrf {vrf-name | all
| default | management}]
Displays the list of OSPFv2 neighbors.
Displays the list of OSPFv2 link-state requests.
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Monitoring OSPFv2
Command show ip ospf retransmission-list
neighbor-id interface
-
type number
[vrf
{vrf-name | all | default | management}]
Purpose
Displays the list of OSPFv2 link-state retransmissions.
show ip ospf route [ospf-route]
[summary] [vrf {vrf-name | all | default |
management}]
show ip ospf summary-address [vrf
{vrf-name | all | default | management}]
Displays the internal OSPFv2 routes.
Displays information about the OSPFv2 summary addresses.
Displays information about OSPFv2 virtual links.
show ip ospf virtual-links [brief] [vrf
{vrf-name | all | default | management}]
show ip ospf vrf
{vrf-name | all | default |
management}
show running-configuration ospf
Displays information about the VRF-based OSPFv2 configuration.
Displays the current running OSPFv2 configuration.
Monitoring OSPFv2
To display OSPFv2 statistics, use the following commands:
Command Purpose
show ip ospf policy statistics area area-id
filter-list
{in | out} [vrf {vrf-name | all |
default | management}]
Displays the OSPFv2 route policy statistics for an area.
show ip ospf policy statistics redistribute
{bgp id | direct | eigrp id | isis id | ospf id |
rip id | static} [vrf {vrf-name | all | default
| management}]
Displays the OSPFv2 route policy statistics.
show ip ospf statistics [vrf {vrf-name | all
| default | management}]
Displays the OSPFv2 event counters.
show ip ospf traffic
[interface
-
type
number] [vrf {vrf-name | all | default |
management}]
Displays the OSPFv2 packet counters.
Configuration Examples for OSPFv2
The following example shows how to configure OSPFv2: feature ospf router ospf 201 router-id 290.0.2.1
interface ethernet 1/2 ip router ospf 201 area 0.0.0.10
ip ospf authentication ip ospf authentication-key 0 mypass
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Additional References
OSPF RFC Compatibility Mode Example
The following example shows how to configure OSPF to be compatible with routers that comply with
RFC 1583:
Note
You must configure RFC 1583 compatibility on any VRF that connects to routers running only RFC1583 compatible OSPF.
switch# configure terminal switch(config)# feature ospf switch(config)# router ospf Test1 switch(config-router)# rfc1583compatibility switch(config-router)# vrf A switch(config-router-vrf)# rfc1583compatibility
Additional References
For additional information related to implementing OSPF, see the following sections:
•
•
Related Documents
Related Topic
Keychains
OSPFv3 for IPv6 networks
Route maps
Document Title
Cisco Nexus 9000 Series NX-OS Security Configuration Guide
Chapter 6, “Configuring OSPFv3”
Chapter 15, “Configuring Route Policy Manager”
MIBs
MIBs
MIBs related to OSPFv2
MIBs Link
To locate and download supported MIBs, go to the following URL: ftp://ftp.cisco.com/pub/mibs/supportlists/nexus9000/Nexus9000MI
BSupportList.html
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Key features
- Supports OSPFv2 for IPv4 networks
- Link-state protocol
- Builds routing table
- Sends hello packets to discover routers
- Synchronizes link-state databases with neighbors
- Supports advanced features like route redistribution and summarization
- Provides high availability and graceful restart