3com 3031 Instruccion De Instalación

After above configuration, due to the fact that the MED attribute of route 1.0.0.0 
discovered by Router C is less than that of Router B, Router D will first select the 
route 1.0.0.0 from Router C.

If the MED attribute of Router A is not configured, the local priority on Router C is 
configured as follows:

1 Configure the local priority attribute of Router C

a Add ACL 2001 on Router C and permit network 1.0.0.0

[Router C]acl number 2001

[Router C-acl-basic-2001]rule permit source 1.0.0.0 0.255.255.255

b Define the route policy with the name of “localpref”. Set the local preference 

matching ACL 2001 as 200, and that of not matching as 100.

[Router C]route-policy localpref permit node 10

[Router C-route-policy]if-match acl 2001

[Router C-route-policy]apply local-preference 200

[Router C-route-policy]route-policy localpref permit node 20

[Router C-route-policy]apply local-preference 100

[Router C]quit

c Apply such route policy to the BGP neighbor 193.1.1.1 (Router A)

[RouterC] bgp 200

[RouterC-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 Router C is greater than that of Router B (Router B is not 
configured with local preference attribute, 100 by default), Router D will also first 
select the route 1.0.0.0 from Router C.

Fault 1: The neighboring relationship cannot be established (The Established state 
cannot be entered).

■

The establishment of BGP neighborhood needs the router able to establish TCP 
session 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 

has been configured. By default, the router uses the optimal local interface to 
establish the TCP connection, rather than uses the loopback interface.

■

If it is the EBGP neighbor not directly connected physically, check whether the 

 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 

 command to check 

if there is available route in the routing table to the neighbor.