Troubleshooting OSPF

Useful commands

show ip ospf interface brief  

show ip ospf neighbor

debug ip ospf hello

debug ip ospf adj

common ospf problems

1) NETWORK TYPES, plus HELLO AND DEAD TIMERS

check compatibility on ospf network-types and timers

 Broadcast to Broadcast                                 (DR)

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

 Non-Broadcast to Non-Broadcast            (DR)

 Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5

 Point-to-Point to Point-to-Point                             (NO DR)

 Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

 Point-to-Multipoint to Point-to-Multipoint       (NO DR)

 Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5

Network types with DR can be mixed. Likewise network types with NON DR can be mixed. However the hello timers will need to be tweaked and matched  e.g.  ip ospf hello-interval 10

debug ip ospf hello with point-to-point towards point-to-multipoint

*Mar  1 00:32:29.935: OSPF: Mismatched hello parameters from 1.1.1.2

*Mar  1 00:32:29.935: OSPF: Dead R 40 C 120, Hello R 10 C 30

Notes

i)if you mix network types that have compatible timers then the adjacency may well form, but the route exchange wont work as expected!!!!

ii) A  DR and BDR on a frame relay network must have full reachability with other routers in the region. Make sure of the neighbour command to achieve this.  

2) MASK

The network mask must match on adjoining interfaces (unless its a point to point ospf network type).

This will be highlighted by debug ip ospf hello

*Mar  1 00:18:21.327: OSPF: Mismatched hello parameters from 1.1.1.2

*Mar  1 00:18:21.327: OSPF: Dead R 40 C 40, Hello R 10 C 10  Mask R 255.255.255.0 C 255.255.255.128

3) MTU

Interface mtu's must match.   This can be highlighted by debug ip ospf adj

*Mar  1 00:14:15.879: OSPF: Rcv DBD from 2.2.2.2 on FastEthernet0/0

       seq 0x9C9 opt 0x52 flag 0x7 len 32  mtu 500 state EXSTART

4) AREA ID AND STUB SETTINGS

If using stub areas. All routers in area must be configured that way.

5) AUTHENTICATION

Using debug ip ospf adj

*Mar  1 00:07:26.607: OSPF: Rcv pkt from 10.10.10.2, FastEthernet0/0 : Mismatch Authentication Key - Message Digest Key 1

*Mar  1 00:07:30.843: OSPF: Send with youngest Key 1

*Mar  1 00:07:30.843: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0 from 10.10.10.1

6) ROUTER IDS MUST BE UNIQUE

*Mar  1 00:02:43.899: %OSPF-4-DUP_RTRID_NBR: OSPF detected duplicate

router-id 1.1.1.1 from 10.10.10.1 on interface FastEthernet0/0