3Com Switch 7757, Configuration Manual

Page: 376 / 940

376 C
HAPTER
36: BGP C
ONFIGURATION
(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.
BGP Error
Configuration
Example
BGP Peer Connection
Establishment Error
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.
■
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 through the neighbor device, check whether there is a route
to the neighbor in the routing table.
■
If you can ping through the neighbor device, check whether 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) must not be conflict
with any 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 actual interface network segment. This may result in
unsuccessful route import or wrong import, and may cause routing error in some
network trouble situations.