Troubleshooting Bgp Configuration - H3C S7500 Series Operation Manual

Operation Manual – Routing Protocol
H3C S7500 Series Ethernet Switches
[SwitchC-route-policy] if-match acl 2000
[SwitchC-route-policy] apply local-preference 200
[SwitchC-route-policy] quit
[SwitchC] route-policy localpref permit node 20
[SwitchC-route-policy] apply local-preference 100
[SwitchC-route-policy] quit
Apply this routing policy to the inbound traffic flows coming from BGP neighbor
193.1.1.1 (Switch A).
[SwitchC] bgp 200
[SwitchC-bgp] peer 193.1.1.1 route-policy localpref import
In this case, because the local preference value of the route 1.0.0.0 learned by Switch
C is 200, which is greater than that of the route 1.0.0.0 learned by Switch B (Switch B
does not configure the local preference attribute, the default value is 100), Switch D
still chooses the route 1.0.0.0 coming from Switch C first.

6.10 Troubleshooting BGP Configuration

Symptom 1: A BGP neighbor relationship cannot be established; that is, the
connection with the opposite peer cannot be established.
Solution: The BGP neighbor establishment process requires using port 179 to
establish a TCP session and exchanging Open messages correctly. You can follow
these steps to solve the problem:
Check the AS number of the neighbor.
Check the IP address of the neighbor.
For an EBGP neighbor not directly connected, verify that the peer
ebgp-max-hop command is used.
Use the ping command to check the TCP connection. As a router may have
more than one interface to reach the peer, you should use the ping -a ip-address
expanded command to specify a source IP address for sending ping packets.
If you cannot ping the neighbor device successfully, verify that there is a route to
the neighbor in the routing table.
If you can ping the neighbor device successfully, verify that an ACL is configured
to inhibit TCP port 179. If yes, cancel the inhibition of port 179.
Symptom 2: After you use the network command to import the routes discovered by
IGP to BGP, the BGP routes cannot be successfully advertised.
Solution: For a route to be successfully imported into BGP, it is required that the route
(including the destination network segment and mask) should be consistent with a
route in the routing table. For example, a route to the network segment 10.1.1.0/24
exists in the routing table. If a route to 10.0.0.0/8 or other similar segment is imported,
an import error will occur. If OSPF is used, when you use the network command to
import a bigger network segment, the router will change the route according to the
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Chapter 6 BGP Configuration