11.5.3 Checking neighboring router information

You can use the show ip ospf neighbor operation command to check the IP address, neighbor state, router ID, and priority of neighboring routers.

On an OSPF interface, the designated router (DR) forms adjacencies with the other routers. You can monitor its progress by checking the State field in the command output.

Full appears as the status of routers that have formed an adjacency. Otherwise, the router is in the process of forming an adjacency with the designated router and cannot learn OSPF routes at its interfaces.

You can examine the neighboring routers in more detail by executing the show ip ospf interface and show ip ospf neighbor detail operation commands. The command output includes the interface state, network type, and connectivity with neighboring routers.

• Make sure that the OSPF network type of the interface is the same as that of its neighboring routers.

• When DR or P to P appears as the interface state, make sure that the status of each neighboring router in the neighbor list is Full.

  • A value other than Full indicates that the interface has not formed an adjacency with the neighboring router. Check the neighboring routers.

• When BackupDR or DR Other appears as the interface state, check whether the neighbor list contains a router that is eligible to be elected the DR.

  • If a DR exists in the neighbor list but its neighboring routers have a status other than Full, this indicates that the interface has not formed an adjacency with the neighboring router. Check the neighboring routers.

  • If no DR exists, this might indicate that no priority has been assigned to the Switch or its neighbors. Check the priority setting for the switch and neighboring routers.

>show ip ospf neighbor
Date 20XX/07/14 12:00:00 UTC
Domain: 1
Area: 0
Address         State                RouterID      Priority Interface
172.16.10.11    Full/BackupDR        172.16.1.1          1  172.16.10.10
172.16.10.12    Full/DR Other        172.16.1.2          1  172.16.10.10
172.126.110.111 Exch Start/BackupDR  172.126.123.111     1  172.126.120.130

>show ip ospf interface 192.168.50.1
Date 20XX/05/30 12:00:00 UTC 
Domain: 1
Index: 2, Name: VLAN0010, Address: 192.168.50.1, State: P to P
Auth Type: Simple
MTU: 1436, DDinPacket: 70, LSRinPacket: 117, ACKinPacket: 70
Router ID: 192.168.50.1, Network Type: P to P
Area: 0, DR: none, Backup DR: none
Priority: 0, Cost: 1
Transmit Delay: 1s
Intervals:
  Hello: 10s, Dead: 40s, Retransmit: 5s
 
Neighbor List (1):
Address         State      RouterID     Priority DR             Backup DR
192.168.50.2    Full       192.168.50.2    0     none           none
>

>show ip ospf neighbor detail
Date 20XX/05/30 12:00:00 UTC
Domain: 1
Area: 0
Interface Address: 172.16.10.10, Interface State: BackupDR
    Interface Name: VLAN0020
    Neighbor Router ID: 172.16.1.1, Neighbor State: Full/DR
    Neighbor Address: 172.16.10.11, Priority: 1, Poll Interval: 0s
    Last Hello: 6s, Last Exchange: 45d 12h
    DR: 172.16.10.11, Backup DR: 172.16.10.10
    DS: 0, LSR: 0, Retrans: 0, <Master>
 
    Neighbor Router ID: 172.16.1.2, Neighbor State: Full/DR Other
    Neighbor Address: 172.16.10.12, Priority: 1, Poll Interval: 0s
    Last Hello:  3s, Last Exchange:  1s
    DR: 172.16.10.11, Backup DR: 172.16.10.10
    DS: 0, LSR: 0, Retrans: 0, <>
>