show ip ospf interface briefshow ip ospf neighbor
debug ip ospf hello
debug ip ospf adj
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
*Mar 1 00:32:29.935: OSPF: Mismatched hello parameters from 18.104.22.168
*Mar 1 00:32:29.935: OSPF: Dead R 40 C 120, Hello R 10 C 30
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.
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 22.214.171.124*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
Interface mtu's must match. This can be highlighted by debug ip ospf adj
*Mar 1 00:14:15.879: OSPF: Rcv DBD from 126.96.36.199 on FastEthernet0/0seq 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.
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 188.8.131.52 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 duplicaterouter-id 184.108.40.206 from 10.10.10.1 on interface FastEthernet0/0