Bgp Troubleshooting - 3Com 7700 Configuration Manual

BGP Troubleshooting

[Switch C-acl-basic-1] rule permit source 1.0.0.0 0.255.255.255
Define the route policy with the name of localpref, of those, the local
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preference matching ACL 1 is set as 200, and that of not matching is set as
100.
[Switch C] route-policy localpref permit node 10
[Switch C-route-policy] if-match acl 1
[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 such route policy to the BGP neighbor 193.1.1.1 (Switch A)
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[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 more 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.
The neighborhood cannot be established (the established state cannot be
entered).
Do the following:
The establishment of BGP neighborhood requires that the router be able to
establish a 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.
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Check whether the neighbor's IP address is correct.
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If you are using the Loopback interface, check whether the connect-source
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loopback 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
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ebgp-max-hop has been configured.
Use the ping command to check whether the TCP connection is normal. Since
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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 display ip routing-table command to check if
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there is available route in the routing table to the neighbor.
If the Ping operation succeeds, check whether there is an ACL denying TCP port
179. If the ACL is configured, cancel the denying of port 179.
BGP 141