There are some situations where a customer wants to connect to a service provider‘s BGP or MPLS VPN network using the same AS number at more than one site. This can create a problem because it is the default BGP procedure to reject routes from the same AS. One solution to this problem is to configure a PE router to override the AS_PATH attribute of its BGP neighbor. This is accomplished by configuring the neighbor as-override command on the PE. When this is enabled, the PE device determines when the AS_PATH attribute in a route intended for a neighbor CE contains the same AS number as the CE. When this is determined, the PE device substitutes its own AS number for the CEs in the AS_PATH attribute. The CE is then able to receive the route. The following additional conditions apply when this feature is in effect:
The following command configures the PE device to replace its attached CEs AS number with its own AS number. BGP neighbor at IP address 10.33.36.2 the configuration of PE 2 required to enable Autonomous System number override for the BGP neighbor CE 2.
To configure a PE device to replace its attached CEs AS number with its own AS number, enter the following commands at the VRF level of the BGP Config level.
(config-bgp-vpnv4u)# neighbor 10.33.36.2 as-override