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Implementing OSPF on Cisco IOS XR Software
Open Shortest Path First (OSPF) is an Interior Gateway Protocol (IGP) developed by the OSPF working
group of the Internet Engineering Task Force (IETF). Designed expressly for IP networks, OSPF
supports IP subnetting and tagging of externally derived routing information. OSPF also allows packet
authentication and uses IP multicast when sending and receiving packets.
Implementing OSPF version 3 (OSPFv3) expands on OSPF Version 2, to provide suppor
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Implementing OSPF on Cisco IOS XR Software Contents Contents � Prerequisites for Implementing OSPF on Cisco IOS XR Software, page RC-170 � Information About Implementing OSPF on Cisco IOS XR Software, page RC-170 � How to Implement OSPF on Cisco IOS XR Software, page RC-183 � Configuration Examples for Implementing OSPF on Cisco IOS XR Software, page RC-236 � Where to Go Next, page RC-241 � Additional References, page RC-243 Prerequisites for Implementing OSPF on Cisco IOS XR Software The fo
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software � Route Authentication Methods for OSPF Version 2, page RC-177 � Neighbors and Adjacency for OSPF, page RC-178 � Designated Router (DR) for OSPF, page RC-178 � Default Route for OSPF,, page RC-179 � Link-State Advertisement Types for OSPF Version 2, page RC-179 � Link-State Advertisement Types for OSPFv3, page RC-179 � Virtual Link and Transit Area for OSPF, page RC-180 � Route Redistribut
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software The networking devices running OSPF detect topological changes in the network, flood link-state updates to neighbors, and quickly converge on a new view of the topology. Each OSPF router in the network soon has the same topological view again. OSPF allows multiple equal-cost paths to the same destination. Since all link-state information is flooded and used in the SPF calculation, multi
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software � Not-so-stubby area (NSSA)—RFC 1587 is supported. � OSPF over demand circuit—RFC 1793 is supported. Comparison of Cisco IOS XR OSPFv3 and OSPFv2 Much of the OSPFv3 protocol is the same as in OSPFv2. OSPFv3 is described in RFC 2740. The key differences between the Cisco IOS XR OSPFv3 and OSPFv2 protocols are as follows: � OSPFv3 expands on OSPFv2 to provide support for IPv6 routing prefi
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software Tip Understanding hierarchical CLI and CLI inheritance saves you considerable configuration time. See the “Configuring Authentication at Different Hierarchical Levels for OSPF Version 2” section on page 194 to understand how to implement these fundamentals. In addition, Cisco IOS XR examples are provided in the “Configuration Examples for Implementing OSPF on Cisco IOS XR Software” sect
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software Areas Areas allow the subdivision of an autonomous system into smaller, more manageable networks or sets of adjacent networks. As shown in Figure 10, autonomous system A consists of three areas: Area 0, Area 1, and Area 2. OSPF hides the topology of an area from the rest of the autonomous system. The network topology for an area is visible only to routers inside that area. When OSPF rou
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software Routers The OSPF network is composed of ABRs, ASBRs, and interior routers. Area Border Routers An area border routers (ABR) is a router with multiple interfaces that connect directly to networks in two or more areas. An ABR runs a separate copy of the OSPF algorithm and maintains separate routing data for each area that is attached to, including the backbone area. ABRs also send configu
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software � The primary IPv4 address of the interface specified by the OSPF router-id command. � The 32-bit numeric value specified by the router-id command in global configuration mode. (This value must be an IPv4 address assigned to an interface on this router.) � By using the highest IPv4 address on a loopback interface in the system if the router is booted with saved loopback address configu
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software Authentication Strategies Authentication can be specified for an entire process or area, or on an interface or a virtual link. An interface or virtual link can be configured for only one type of authentication, not both. Authentication configured for an interface or virtual link overrides authentication configured for the area or process. If you intend for all interfaces in an area to us
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software Default Route for OSPF, Type 5 (ASE) LSAs are generated and flooded to all areas except stub areas. For the routers in a stub area to be able to route packets to destinations outside the stub area, a default route is injected by the ABR attached to the stub area. The cost of the default route is 1 (default) or is determined by the value specified in the default-cost command. Link-State
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software � Interarea-prefix LSA for ABRs (Type 3)—Advertises internal networks to routers in other areas (interarea routes). Type 3 LSAs may represent a single network or set of networks aggregated into one prefix. Only ABRs generate Type 3 LSAs. In OSPFv3, addresses for these LSAs are expressed as “prefix and prefix length” instead of “address and mask.” The default route is expressed as a pre
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software In the case in which an area cannot be connected to Area 0, you must configure a virtual link between that area and Area 0. The two endpoints of a virtual link are ABRs, and the virtual link must be configured in both routers. The common nonbackbone area to which the two routers belong is called a transit area. A virtual link specifies the transit area and the router ID of the other vir
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Implementing OSPF on Cisco IOS XR Software Information About Implementing OSPF on Cisco IOS XR Software The interval at which the SPF calculations occur is chosen dynamically and based on the frequency of topology changes in the network. The chosen interval is within the boundary of the user-specified value ranges. If network topology is unstable, SPF throttling calculates SPF scheduling intervals to be longer until topology becomes stable. SPF calculations occur at the interval set by t
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Implementing OSPF on Cisco IOS XR Software How to Implement OSPF on Cisco IOS XR Software through intelligent line cards while the standby Route Processor (RP) assumes control from the failed RP. The ability of line cards to remain up through a failover and to be kept current with the Forwarding Information Base (FIB) on the active RP is key to Cisco IOS XR NSF operation. Routing protocols, such as OSPF, run only on the active RP or DRP and receive routing updates from their neighbor rout
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Implementing OSPF on Cisco IOS XR Software How to Implement OSPF on Cisco IOS XR Software � Controlling the Frequency that the Same LSA Is Originated or Accepted for OSPF, page RC-197 (optional) � Creating a Virtual Link with MD5 Authentication to Area 0 for OSPF, page RC-199 (optional) � Summarizing Subnetwork LSAs on an OSPF ABR, page RC-203 (optional) � Redistributing Routes from One IGP into OSPF, page RC-205 (optional) � Configuring OSPF Shortest Path First Throttling, page RC-209 (opt
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Implementing OSPF on Cisco IOS XR Software How to Implement OSPF on Cisco IOS XR Software DETAILED STEPS Command or Action Purpose Step 1 configure Enters global configuration mode. Example: RP/0/RP0/CPU0:router# configure Step 2 router ospf process-name Enables OSPF routing for the specified routing process and or places the router in router configuration mode. router ospfv3 process-name or Enables OSPFv3 routing for the specified routing process Example: and places the router in router o
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Implementing OSPF on Cisco IOS XR Software How to Implement OSPF on Cisco IOS XR Software Command or Action Purpose log adjacency changes [detail] [enable | Step 7 (Optional) Requests notification of neighbor changes. disable] � By default, this feature is enabled. � The messages generated by neighbor changes are Example: considered notifications, which are categorized as RP/0/RP0/CPU0:router(config-ospf-ar-if)# log severity Level 5 in the logging console command. The adjacency changes
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Implementing OSPF on Cisco IOS XR Software How to Implement OSPF on Cisco IOS XR Software 6. stub or nssa 7. default-cost cost 8. end or commit 9. Repeat this task on all other routers in the stub area or NSSA. DETAILED STEPS Command or Action Purpose Step 1 configure Enters global configuration mode. Example: RP/0/RP0/CPU0:router# configure router ospf process-name Step 2 Enables OSPF routing for the specified routing process and or places the router in router configuration mode. router
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Implementing OSPF on Cisco IOS XR Software How to Implement OSPF on Cisco IOS XR Software Command or Action Purpose stub [no-summary] Step 5 Defines the nonbackbone area as a stub area. or � See the “Configuring Stub and Not-so-Stubby Area nssa [no-redistribution] Types” section on page 186. [default-information-originate] [no-summary] � Specify the no-summary keyword to further reduce the number of LSAs sent into a stub area. This keyword Example: prevents the ABR from sending summary l
