Troubleshooting Bgp - 3Com 8807 Configuration Manual

390 C 33: BGP C
HAPTER ONFIGURATION
[Switch C] acl number 2000
[Switch C-acl-basic-2000] rule permit source 1.0.0.0 0.255.255.255
[Switch C-acl-basic-2000] rule deny source any
Define a route policy named Localpref, and set the local preference of routes
matching ACL 2000 to 200, and that of routes not matching to 100.
[Switch C] route-policy localpref permit node 10
[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.

Troubleshooting BGP

Symptom 1: The neighborhood 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 using the Loopback interface, check whether the connect-source loopback
command has been configured. By default, the router uses the optimal local
interface to establish the TCP connection, not using the loopback interface.
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.