Example: Using a Single AS Number for All CE Sites

If you want to use the same AS number for all of your CE sites, you can substitute a PE router’s autonomous system number for that of a neighbor by specifying the neighbor’s IP address in the neighbor as-override command. If you fail to do this, the CE router recognizes its AS in the AS path of received routes and determines it has discovered a routing loop; the routes are rejected.

In the following example, the router’s AS number of 777 overrides the neighboring router's AS number of 100.

host1:vr1(config)#router bgp 777 host1:vr1(config-router)#neighbor 172.16.20.10 remote-as 100 host1:vr1(config-router)#neighbor 172.16.20.10 update-source loopback0 host1:vr1(config-router)#address-family ipv4 vrf vpn1 host1:vr1(config-router-af)#neighbor 172.25.14.12 remote-as 100 host1:vr1(config-router-af)#neighbor 172.25.14.12 as-override

Note: To apply the new policy to routes that are already present in the BGP routing table, you must use the clear ip bgp command to perform a soft clear or hard clear of the current BGP session.

Behavior is different for outbound policies configured for peer groups for which you have enabled Adj-RIBs-Out. If you change the outbound policy for such a peer group and want to fill the Adj-RIBs-Out table for that peer group with the results of the new policy, you must use the clear ip bgp peer-group command to perform a hard clear or outbound soft clear of the peer group. You cannot merely perform a hard clear or outbound soft clear for individual peer group members because that causes BGP to resend only the contents of the Adj-RIBs-Out table.