No BGP peer relationship established

Symptom

Display BGP peer information using the show ip bgp neighbor command. A connection to a peer has not been established.

Analysis

To become BGP peers, any two routers need to establish a TCP session using port 179 and exchange open messages successfully.

Solution

1. Use the show ip bgp neighbor command to verify the peer’s IP address.

2. If the loopback interface is used, check whether the neighbor connect interface command is configured.

3. If the peer is a non-direct eBGP peer, check whether the neighbor ebgp multihop command is configured.

4. Check whether a route to the peer is available in the routing table.

5. Use the ping command to check connectivity.

6. Use the display tcp status command to check the TCP connection.

7. Check whether an ACL is configured that disables TCP port 179.