Configuring a PE to allow routes with its AS number

BGP rejects routes that contain its own AS number within its AS_PATH attribute to prevent routing loops. In an MPLS or VPN hub and spoke topology this can stop legitimate routes from being accepted. The allowas-in command fixes this problem by allowing the user to set a parameter that disables the AS_PATH check function for routes learned from a specified location.

To configure a PE to disable the AS_PATH check function for routes sent to it by its BGP neighbor (a CE device with the IP address for a maximum limit of three occurrences of the route, enter the following command at the BGP VRF configuration level.

(config-bgp-ipv4u-vrf)# neighbor allowas-in 3

Syntax: [no] neighbor IPaddress allowas-in asn_limit

The IPaddress is the IP address of the neighbor CE device from which the PE device can accept routes that have the same AS number.

The asn_limit value prevents loops by limiting the number of occurrences that the PEs AS number can be accepted in routes that are received from the specified device.