Cisco BGP-4 Command and Configuration Handbook

Syntax Description: This command has no arguments.

Purpose: Use to debug the formation of the BGP neighbor relationship.

Cisco IOS Software Release: 10.0

Configuration Example

In Figure 16-1, Router B has been configured with the wrong AS number for Router A.

Router A router bgp 1 neighbor 172.17.1.1 remote-as 2 ___________________________________________________________________________ Router B router bgp 2 neighbor 172.17.1.2 remote-as 1

Use debug ip bgp to identify the problem with the formation of the neighbor relationship between Routers A and B:

rtrB# debug ip bgp rtrB# clear ip bgp * 1d03h: BGP: 172.17.1.2 went from Idle to Active 1d03h: BGP: 172.17.1.2 open active, delay 5492ms 1d03h: BGP: 172.17.1.2 open active, local address 172.17.1.1 1d03h: BGP: 172.17.1.2 went from Active to OpenSent 1d03h: BGP: 172.17.1.2 sending OPEN, version 4, my as: 2 1d03h: BGP: 172.17.1.2 send message type 1, length (incl. header) 41 1d03h: BGP: 172.17.1.2 rcv message type 1, length (excl. header) 10 1d03h: BGP: 172.17.1.2 rcv OPEN, version 4 1d03h: BGP: 172.17.1.2 rcv OPEN w/ OPTION parameter len: 0 1d03h: BGP: 172.17.1.2 bad OPEN, remote AS is 1, expected 2 1d03h: BGP: 172.17.1.2 went from OpenSent to Closing 1d03h: BGP: 172.17.1.2 sending NOTIFICATION 2/2 (peer in wrong AS) 2 bytes 0001 1d03h: BGP: 172.17.1.2 local error close, erroneous BGP update received 1d03h: BGP: 172.17.1.2 went from Closing to Idle 1d03h: BGP: 172.17.1.2 closing

Correct the remote AS number in the neighbor statement on Router B, but use an incorrect IP address for Router A:

Router B router bgp 2 neighbor 172.17.1.3 remote-as 1

Clear the connection and observe the debug output:

rtrB# debug ip bgp rtrB# clear ip bgp * 1d04h: BGP: 172.17.1.3 open active, local address 172.17.1.1 1d04h: BGP: 172.17.1.3 open failed: Connection timed out; remote host not responding