3com 8807 User Guide

C

HAPTER

 31: OSPF C

ONFIGURATION

Symptom 1: OSPF has been configured in accordance with the earlier-mentioned 
steps, but OSPF on the router cannot run normally.

Solution: Check according to the following procedure.

Local troubleshooting: Check whether the protocol between two directly 
connected routers is in normal operation. The normal sign is the peer state 
machine between the two routers reaches the FULL state. (Note: On a broadcast 
network, if the interfaces for two routers are in DROther state, the peer state 
machines for the two routers are in 2-way state, instead of FULL state. The peer 
state machine between DR/BDR and all the other routers is in FULL state.

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Execute the display ospf peer command to view peers.

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Execute the display ospf interface command to view OSPF information on 
the interface.

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Check whether the physical connections and the lower layer protocol operate 
normally. You can execute the ping command to test. If the local router cannot 
ping the peer router, it indicates that faults have occurred to the physical link 
and the lower layer protocol.

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If the physical link and the lower layer protocol are normal, check the OSPF 
parameters configured on the interface. The parameters should be the same 
parameters configured on the router adjacent to the interface. The same area 
ID 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.)

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Ensure that the dead timer on the same interface is at least four times the value 
of the Hello timer.

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If the network type is broadcast, there must be at least one interface with a 
priority greater than zero.

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If an area is set as the stub area, to which the routers are connected. The area 
on these routers must be also set as the stub area.

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The same interface type should be adopted for the neighboring routers.

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If more than two areas are configured, at least one area should be configured 
as the backbone area (that is to say, the area ID is 0).

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Ensure that the backbone area is connected to all other areas.

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The virtual links do not pass through the stub area.

Global troubleshooting: If OSPF cannot discover the remote routes yet in the case 
that the above steps are correctly performed, proceed to check the following 
configurations.

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If more than two areas are configured on a router, at least one area should be 
configured 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 to 
belong to two areas. In which, RTB also belongs to area0, which is compliant with 
the 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 Area2 
and Area0 (backbone area) is connected.