Troubleshooting Bgp - H3C S9500 Series Operation Manual

Operation Manual – BGP
H3C S9500 Series Routing Switches
[Switch C-route-policy] if-match acl 2000
[Switch C-route-policy] apply local-preference 200
[Switch C-route-policy] route-policy localpref permit node 20
[Switch C-route-policy] apply local-preference 100
[Switch C-route-policy] quit
Apply this route policy to ingress traffic from BGP neighbor 193.1.1.1 (Switch A).
[Switch C] bgp 200
[Switch C-bgp] peer 193.1.1.1 route-policy localpref import
By then, due to the fact that the Local preference attribute value (200) of the route
1.0.0.0 learned by Switch C is higher than that of Switch B (Switch B is not configured
with local Preference attribute, 100 by default), Switch D will also first select the route
1.0.0.0 from Switch C.

1.5 Troubleshooting BGP

Symptom 1: The neighbor relationship cannot be established (The Established state
cannot be entered).
Solution: The establishment of BGP neighborhood needs the router able to establish
TCP connection through port 179 and exchange Open packets correctly. Perform the
check according to the following steps:
Check whether the configuration of the neighbor's AS number is correct.
Check whether the neighbor's IP address is correct.
If it is the EBGP neighbor not directly connected, check whether the peer
ebgp-max-hop command has been configured.
Use the ping command to check whether the TCP connection is normal. Since
one router may have several interfaces able to reach the peer, the extended ping
-a ip-address command should be used to specify the source IP address sending
ping packet.
If the Ping operation fails, use the display ip routing-table command to check if
there is available route in the routing table to the neighbor.
If the Ping operation succeeds, check if there is an ACL denying TCP port 179. If
the ACL is configured, cancel the denying of port 179.
Symptom 2: BGP route cannot be advertised correctly after route of IGP is imported
with the network command.
Solution: Route imported by the network command should be same as a route in the
current routing table, which should include destination segment and mask. Route
covering large network segment cannot be imported. For example, route 10.1.1.0/24
can be imported, while 10.0.0.0/8 may cause error. If Ospf is used, after a large network
segment is imported to the local route by means of the network command, the router
will automatically make changes according to the network segment actually used by
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Chapter 1 BGP Configuration