H3C Technologies H3C S12500-X Series Switches - Manual (Page 299)

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Troubleshooting BGP
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Symptom
Display BGP peer information by using the display bgp peer ipv4 unicast or display bgp peer ipv6
unicast command. The state of the connection to a peer cannot become established.
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Analysis
To become BGP peers, any two routers must establish a TCP connection using port 179 and exchange
Open messages successfully.
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Solution
1. Use the display current-configuration command to verify the current configuration, and verify that
the peer's AS number is correct.
2. Use the display bgp peer ipv4 unicast or display bgp peer ipv6 unicast command to verify that the
peer's IP address/IPv6 address is correct.
3. If a loopback interface is used, verify that the loopback interface is specified with the peer
connect-interface command.
4. If the peer is a non-direct EBGP peer, verify that the peer ebgp-max-hop command is configured.
5. Verify that a valid route to the peer is available.
6. Use the ping command to verify the connectivity to the peer.
7. Use the display tcp verbose or display ipv6 tcp verbose command to verify the TCP connection.
8. Verify that no ACL rule is applied to disable TCP port 179.