Configuring OSPFCisco’s OSPF ImplementationOSPF Configuration Task ListEnable OSPF12Configure OSPF Interface ParametersConfigure OSPF over Different Physical NetworksConfigure Your OSPF Network TypeConfigure Point-to-Multipoint, Broadcast Networks12345Configure OSPF for Nonbroadcast Networks12345Configure OSPF Area ParametersConfigure OSPF Not So Stubby Area (NSSA)Implementation ConsiderationsConfigure Route Summarization between OSPF AreasConfigure Route Summarization when Redistributing Routes into OSPFCreate Virtual LinksGenerate a Default RouteConfigure Lookup of DNS NamesForce the Router ID Choice with a Loopback Interface12Control Default MetricsChange the OSPF Administrative DistancesConfigure OSPF on Simplex Ethernet InterfacesConfigure Route Calculation TimersConfigure OSPF over On Demand Circuits123Implementation ConsiderationsLog Neighbors Going Up or DownChange the LSA Group PacingOriginal LSA BehaviorFigure21 OSPF LSAs on a Single Timer without Group PacingSolutionFigure22 OSPF LSAs on Individual Timers with Group PacingBlock OSPF LSA FloodingIgnore MOSPF LSA PacketsMonitor and Maintain OSPFOSPF Configuration ExamplesOSPF Point-to-Multipoint ExampleFigure23 OSPF Point-to-Multipoint ExampleMollie’s ConfigurationNeon’s ConfigurationPlatty’s ConfigurationJelly’s ConfigurationOSPF Point-to-Multipoint, Broadcast ExampleOSPF Point-to-Multipoint, Nonbroadcast ExampleVariable-Length Subnet Masks ExampleOSPF Routing and Route Redistribution ExamplesBasic OSPF Configuration ExampleBasic OSPF Configuration Example for Internal Router, ABR, and ASBRsComplex Internal Router, ABR, and ASBRs ExampleFigure24 Sample OSPF Autonomous System Network MapRouter A—Internal RouterRouter B—Internal RouterRouter C—ABRRouter D—Internal RouterRouter E—ASBRComplex OSPF Configuration for ABR ExamplesFigure25 Interface and Area Specifications for OSPF Example ConfigurationRoute Map ExamplesChanging OSPF Administrative DistanceFigure26 OSPF Administrative DistanceRouter ARouter BOSPF over On-Demand Routing ExampleFigure27 OSPF over On-Demand CircuitRouter ARouter BLSA Group Pacing ExampleBlock LSA Flooding ExampleIgnore MOSPF LSA Packets ExampleConfiguring OSPF P1C-107Configuring OSPFThis chapter describes how to configure OSPF. For a complete description of the OSPF commandsin this chapter, refer to the “OSPF Commands” chapter of the Network Protocols CommandReference, Part 1. To locate documentation of other commands that appear in this chapter, use thecommand reference master index or search online.Open shortest path first (OSPF) is an IGP developed by the OSPF working group of the InternetEngineering Task Force (IETF). Designed expressly for IP networks, OSPF supports IP subnettingand tagging of externally derived routing information. OSPF also allows packet authentication anduses IP multicast when sending/receiving packets.We support RFC 1253, Open Shortest Path First (OSPF) MIB, August 1991. The OSPF MIB definesan IP routing protocol that provides management information related to OSPF and is supported byCisco routers.For protocol-independent features that include OSPF, see the chapter “Configuring IP RoutingProtocol-Independent Features” in this document.Cisco’s OSPF ImplementationCisco’s implementation conforms to the OSPF Version 2 specifications detailed in the InternetRFC 1583. The list that follows outlines key features supported in Cisco’s OSPF implementation:• Stub areas—Definition of stub areas is supported.• Route redistribution—Routes learned via any IP routing protocol can be redistributed into anyother IP routing protocol. At the intradomain level, this means that OSPF can import routeslearned via IGRP, RIP, and IS-IS. OSPF routes can also be exported into IGRP, RIP, and IS-IS.At the interdomain level, OSPF can import routes learned via EGP and BGP. OSPF routes can beexported into EGP and BGP.• Authentication—Plain text and MD5 authentication among neighboring routers within an area issupported.• Routing interface parameters—Configurable parameters supported include interface output cost,retransmission interval, interface transmitdelay,router priority, router “dead” and hello intervals,and authentication key.• Virtual links—Virtual links are supported.• NSSA areas—RFC 1587.• OSPF over demand circuit—RFC 1793.OSPF Configuration Task ListP1C-108Network Protocols Configuration Guide, Part 1OSPF Configuration Task ListOSPF typically requires coordination among many internal routers, area border routers (routersconnected to multiple areas), and autonomous system boundary routers. At a minimum, OSPF-basedrouters or access servers can be configured with all default parameter values, no authentication, andinterfaces assigned to areas. If you intend to customize your environment, you must ensurecoordinated configurations of all routers.To configure OSPF, complete the tasks in the following sections. Enabling OSPF is mandatory; theother tasks are optional, but might be required for your application.• Enable OSPF• Configure OSPF Interface Parameters• Configure OSPF over Different Physical Networks• Configure OSPF Area Parameters• Configure OSPF Not So Stubby Area (NSSA)• Configure Route Summarization between OSPF Areas• Configure Route Summarization when Redistributing Routes into OSPF• Create Virtual Links• Generate a Default Route• Configure Lookup of DNS Names• Force the Router ID Choice with a Loopback Interface• Control Default Metrics• Change the OSPF Administrative Distances• Configure OSPF on Simplex Ethernet Interfaces• Configure Route Calculation Timers• Configure OSPF over On Demand Circuits• Log Neighbors Going Up or Down• Change the LSA Group Pacing• Block OSPF LSA Flooding• Ignore MOSPF LSA Packets• Monitor and Maintain OSPFIn addition, you can specify route redistribution; see the task “Redistribute Routing Information” inthe chapter “Configuring IP Routing Protocol-Independent Features” for information on how toconfigure route redistribution.Enable OSPF Configuring OSPF P1C-109Enable OSPFAs with other routing protocols, enabling OSPF requires that you create an OSPF routing process,specify the range of IP addresses to be associated with the routing process, and assign area IDs to beassociated with that range of IP addresses. Use the following commands, starting in globalconfiguration mode:Configure OSPF Interface ParametersOur OSPF implementation