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
-
Use the
show ip bgp neighbor
command to verify the peer’s IP address. -
If the loopback interface is used, check whether the
neighbor connect interface
command is configured. -
If the peer is a non-direct eBGP peer, check whether the
neighbor ebgp multihop
command is configured. -
Check whether a route to the peer is available in the routing table.
-
Use the
display tcp status
command to check the TCP connection. -
Check whether an ACL is configured that disables TCP port 179.