Why do BGP peer relationships fail to be established?
Perform the following operations to locate the fault:
1. Verify that the AS number of the peer interface is correct.
2. Verify that the IP address of the peer interface is correct.
3. If the peer device is a loopback interface, verify that the peer connect-interface command is configured. By default, a router uses the optimal local interface, rather than the loopback interface, to establish the TCP connection.
4. If the peer is an indirectly connected EBGP peer, verify that the peer ebgp-max-hop command is configured on the EBGP peer.
5. Check whether the TCP connection is normal by running the ping command. As one router may have multiple interfaces connected to the peer, run the ping -a ip-address command to specify the source IP address of ping packets.
If the ping operation fails, run the display ip routing-table command to check whether the routing table contains a reachable route to the peer.
If the ping operation succeeds, check whether an ACL is configured to prohibit packets from passing through TCP port 179. If so, cancel the prohibition settings.