336 CHAPTER 31: OSPF C ONFIGURATIONTroubleshooting OSPFFaultsSymptom 1: OSPF has been configured in accordance with the earlier-mentionedsteps, but OSPF on the router cannot run normally.Solution: Check according to the following procedure.Local troubleshooting: Check whether the protocol between two directlyconnected routers is in normal operation. The normal sign is the peer statemachine between the two routers reaches the FULL state. (Note: On a broadcastnetwork, if the interfaces for two routers are in DROther state, the peer statemachines for the two routers are in 2-way state, instead of FULL state. The peerstate machine between DR/BDR and all the other routers is in FULL state.■ Execute the display ospf peer command to view peers.■ Execute the display ospf interface command to view OSPF information onthe interface.■ Check whether the physical connections and the lower layer protocol operatenormally. You can execute the ping command to test. If the local router cannotping the peer router, it indicates that faults have occurred to the physical linkand the lower layer protocol.■ If the physical link and the lower layer protocol are normal, check the OSPFparameters configured on the interface. The parameters should be the sameparameters configured on the router adjacent to the interface. The same areaID should be used, and the networks and the masks should also be consistent.(The p2p or virtually linked segment can have different segments and masks.)■ Ensure that the dead timer on the same interface is at least four times the valueof the Hello timer.■ If the network type is broadcast, there must be at least one interface with apriority greater than zero.■ If an area is set as the stub area, to which the routers are connected. The areaon these routers must be also set as the stub area.■ The same interface type should be adopted for the neighboring routers.■ If more than two areas are configured, at least one area should be configuredas the backbone area (that is to say, the area ID is 0).■ Ensure that the backbone area is connected to all other areas.■ The virtual links do not pass through the stub area.Global troubleshooting: If OSPF cannot discover the remote routes yet in the casethat the above steps are correctly performed, proceed to check the followingconfigurations.■ If more than two areas are configured on a router, at least one area should beconfigured as the backbone area.As shown in Figure 86: RTA and RTD are configured to belong to only one area,whereas RTB (Area0 and Area1) and RTC (Area1 and Area 2) are configured tobelong to two areas. In which, RTB also belongs to area0, which is compliant withthe requirement. However, none of the areas to which RTC belongs is Area0.Therefore, a virtual link should be set up between RTC and RTB. Ensure that Area2and Area0 (backbone area) is connected.
