Troubleshooting guide

Troubleshooting

Strategies for Troubleshooting Specific BGP Problems

An AOS device running BGP might not send or receive the routes that it should for several reasons:

• It cannot communicate with a neighbor

• It is not authorized to transmit, or to accept, the routes in question

View BGP neighbors to make certain the neighbor exists by entering the command show ip bgp neighbor

at the Enable mode prompt.

If the AOS device is able to communicate with the neighbor, but it is not receiving the routes that it should,

then BGP filters need to be examined.

Removing Filters

iBGP allows a user to configure policies to filter routes accepted from and advertised to neighbors. These

policies are configured in prefix lists, route maps, and IPv4 ACLs. Since the policies can be quite

complicated, they open room for errors.

One of the first steps in troubleshooting BGP is to remove any inbound or outbound filters from the

neighbor. If the AOS device begins receiving or advertising the expected routes, then the conclusion is that

the filters are causing the problem. The following commands can be issued from BGP Neighbor

Configuration mode to remove the appropriate filter:

Remove a prefix list:

(config-bgp-neighbor)#no prefix-list <name> [in | out]

<name> Specifies the name of the prefix list to be removed.

in Specifies to remove the inbound filter.

out Specifies to remove the outbound filter.

Remove a route map:

(config-bgp-neighbor)#no route-map <name> [in | out]

<name> Specifies the name of the route map to be removed.

in Specifies to remove the inbound filter.

out Specifies to remove the outbound filter.

Typically, soft resets should be used because hard resets can disrupt the network. A hard

reset clears the TCP connection with the specified peers, which results in clearing the table.

This method of clearing is disruptive and causes peer routers to record a route flap for each

route. Refer to Soft Reconfiguration Inbound on page 31 for additional information.