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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.

Example

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

neighbor as-override

Use to enable the use of the same AS number for all CE sites by substituting the current router’s AS number in routing tables for that of the neighboring router.
If you specify a BGP peer group by using the peer-group-name argument, all the members of the peer group inherit the characteristic configured with this command. You cannot override the characteristic for a specific member of the peer group.
New policy values are applied to all routes that are sent (outbound policy) or received (inbound policy) after you issue the command.
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.
Example 1host1:vr1(config-router)#neighbor 192.168.255.255 as-override
Example 2host1(config-router)#neighbor 192.168.1.158 as-override
Use the no version to halt the substitution of the AS numbers. Use the default version to remove the explicit configuration from the peer or peer group and reestablish inheritance of the feature configuration.
See neighbor as-override.

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