In the final section of this chapter, we are going to look at some of the more commonly used OSPF debugging commands. OSPF debugging is enabled using the debug ip ospf command. This command can be used in conjunction with the following additional keywords:
| R1#debug ip ospf ? adj OSPF adjacency events database-timer OSPF database timer events OSPF events flood OSPF flooding hello OSPF hello events lsa-generation OSPF lsa generation mpls OSPF MPLS nsf OSPF non-stop forwarding events packet OSPF packets retransmission OSPF retransmission events spf OSPF spf tree OSPF database tree |
The debug ip ospf adj command prints real-time information on adjacency events. This is a useful troubleshooting tool when troubleshooting OSPF neighbor adjacency problems. Following is a sample of the information that is printed by this command. The example below illustrates how this command can be used to determine that an MTU mismatch is preventing the neighbor adjacency from reaching the FULL state:
| R1#debug ip ospf adj OSPF adjacency events debugging is on R1# *Mar 18 23:13:21.279: OSPF: DR/BDR election on FastEthernet0/0 *Mar 18 23:13:21.279: OSPF: Elect BDR 2.2.2.2 *Mar 18 23:13:21.279: OSPF: Elect DR 1.1.1.1 *Mar 18 23:13:21.279: DR: 1.1.1.1 (Id) BDR: 2.2.2.2 (Id) *Mar 18 23:13:21.283: OSPF: Neighbor change Event on interface FastEthernet0/0 *Mar 18 23:13:21.283: OSPF: DR/BDR election on FastEthernet0/0 *Mar 18 23:13:21.283: OSPF: Elect BDR 2.2.2.2 *Mar 18 23:13:21.283: OSPF: Elect DR 1.1.1.1 *Mar 18 23:13:21.283: DR: 1.1.1.1 (Id) BDR: 2.2.2.2 (Id) *Mar 18 23:13:21.283: OSPF: Rcv DBD from 2.2.2.2 on FastEthernet0/0 seq 0xA65 opt 0x52 flag 0x7 len 32 mtu 1480 state EXSTART *Mar 18 23:13:21.283: OSPF: Nbr 2.2.2.2 has smaller interface MTU *Mar 18 23:13:21.283: OSPF: NBR Negotiation Done. We are the SLAVE *Mar 18 23:13:21.287: OSPF: Send DBD to 2.2.2.2 on FastEthernet0/0 seq 0xA65 opt 0x52 flag 0x2 len 192 *Mar 18 23:13:26.275: OSPF: Rcv DBD from 2.2.2.2 on FastEthernet0/0 seq 0xA65 opt 0x52 flag 0x7 len 32 mtu 1480 state EXCHANGE *Mar 18 23:13:26.279: OSPF: Nbr 2.2.2.2 has smaller interface MTU *Mar 18 23:13:26.279: OSPF: Send DBD to 2.2.2.2 on FastEthernet0/0 seq 0xA65 opt 0x52 flag 0x2 len 192 [Truncated Output] |
From the output above, we can conclude that the MTU on the local router is larger than 1480 bytes because the debug output shows that the neighbor has the smaller MTU value. The recommended solution would be to adjust the smaller MTU value so that both neighbors have the same interface MTU values. This will allow the adjacency to reach the FULL state.
The debug ip ospf lsa-generation command prints information on OSPF LSAs. This command can be used to troubleshoot route advertisement when using OSPF. Following is a sample output of the information that is printed by this command:
| R1#debug ip ospf lsa-generation OSPF summary lsa generation debugging is on R1# R1# *Mar 18 23:25:59.447: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Interface down or detached *Mar 18 23:25:59.511: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from LOADING to FULL, Loading Done *Mar 18 23:26:00.491: OSPF: Start redist-scanning *Mar 18 23:26:00.491: OSPF: Scan the RIB for both redistribution and translation *Mar 18 23:26:00.499: OSPF: max-aged external LSA for summary 150.0.0.0 255.255.0.0, scope: Translation *Mar 18 23:26:00.499: OSPF: End scanning, Elapsed time 8ms *Mar 18 23:26:00.499: OSPF: Generate external LSA 192.168.4.0, mask 255.255.255.0, type 5, age 0, metric 20, tag 0, metric-type 2, seq 0x80000001 *Mar 18 23:26:00.503: OSPF: Generate external LSA 192.168.5.0, mask 255.255.255.0, type 5, age 0, metric 20, tag 0, metric-type 2, seq 0x80000001 *Mar 18 23:26:00.503: OSPF: Generate external LSA 192.168.1.0, mask 255.255.255.0, type 5, age 0, metric 20, tag 0, metric-type 2, seq 0x80000001 *Mar 18 23:26:00.503: OSPF: Generate external LSA 192.168.2.0, mask 255.255.255.0, type 5, age 0, metric 20, tag 0, metric-type 2, seq 0x80000001 *Mar 18 23:26:00.507: OSPF: Generate external LSA 192.168.3.0, mask 255.255.255.0, type 5, age 0, metric 20, tag 0, metric-type 2, seq 0x80000001 *Mar 18 23:26:05.507: OSPF: Generate external LSA 192.168.4.0, mask 255.255.255.0, type 5, age 0, metric 20, tag 0, metric-type 2, seq 0x80000006 *Mar 18 23:26:05.535: OSPF: Generate external LSA 192.168.5.0, mask 255.255.255.0, type 5, age 0, metric 20, tag 0, metric-type 2, seq 0x80000006 |
The debug ip ospf spf command provides real-time information about Shortest Path First algorithm events. This command can be used in conjunction with the following keywords:
| R1#debug ip ospf spf ? external OSPF spf external-route inter OSPF spf inter-route intra OSPF spf intra-route statistic OSPF spf statistics <cr> |
As is the case with all debug commands, consideration should be given to factors such as the size of the network and the resource utilization on the router before debugging SPF events. Following is a sample of the output from the debug ip ospf spf statistic command:
| R1#debug ip ospf spf statistic OSPF spf statistic debugging is on R1# R1#clear ip ospf process Reset ALL OSPF processes? [no]: y R1# R1# *Mar 18 23:37:27.795: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Interface down or detached *Mar 18 23:37:27.859: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from LOADING to FULL, Loading Done *Mar 18 23:37:32.859: OSPF: Begin SPF at 28081.328ms, process time 608ms |