Troubleshooting guide

Example Configurations

Example 6: Configuring Local Preference, MED, and Next-Hop-Self on an AOS

Router with Both iBGP and eBGP Neighbors

The following example illustrates a scenario where an AOS router has both eBGP and iBGP neighbors.

The AOS device in AS 65000 has two eBGP neighbors: Remote Router 1 and Remote Router 2. This

means that there are multiple exit points from the local AS (65000). One exit is through the AOS router

over the Ethernet WAN interface (eth 0/1) to Remote Router 1. Another exit is through the AOS device

over the PPP interface (PPP 1) to Remote Router 2.

The preferred path for traffic originating from the 192.168.1.0 /24 network and destined for the remote

private 172.16.5.0 /24 network is the Metro-Ethernet connection. Since the remote network 172.16.5.0 /24

is advertised by both eBGP neighbors (Remote Routers 1 and 2), the local preference attribute is modified

to ensure that the Metro-Ethernet connection is selected as the best path to the remote network. This

modification is accomplished by creating a route map (SETLOCALPREF) that matches a prefix list

(MATCHPREFIX), which specifies the 172.16.5.0 /24 network. Within this route map, the LOCAL_PREF

attribute is modified to 110, a higher value than the default LOCAL_PREF value of 100. The route map is

applied inbound from the Ethernet WAN eBGP neighbor (192.168.2.2).

The Metro-Ethernet connection is also the preferred path for traffic originating from the remote

172.16.5.0

/24 network inbound to the 192.168.1.0 /24 network. The MED is modified to ensure that the

Metro-Ethernet connection is selected as the best path inbound to the local network. This modification is

accomplished by creating two separate route maps (SETMULTIEXIT1 and SETMULTIEXIT2); each

matching a prefix list (NETWORK) that specifies the 192.168.1.0 /24 network. The MULTI_EXIT_DISC

value in the route map SETMULTIEXIT1 is set to 100, whereas the MULTI_EXIT_DISC value in the

route map SETMULTIEXIT2 is set to 200. SETMULTIEXIT1 is applied outbound to the Ethernet WAN

eBGP neighbor (192.168.2.2). SETMULTIEXIT2 is applied outbound to the T1 eBGP neighbor

(10.10.10.2).

The AOS device has two iBGP neighbors: Local Router 1 and Local Router 2. The next-hop-self

command is used to advertise the IPv4 address of the AOS router (192.168.1.1) to its iBGP neighbors as

the path to reach any of the networks advertised by the eBGP peers.

The route with the highest local preference value is preferred in BGP.

The route with the lowest MED metric value is preferred in BGP.

All iBGP routers are fully meshed for both AS 65000 and AS 65001.