The peer substitute-as command enables AS number substitution. This command enables a device to replace the AS number of the peer specified in the AS_Path attribute with the local AS number.
The undo peer substitute-as command disables AS number substitution.
By default, AS number substitution is disabled.
peer { group-name | ipv4-address | ipv6-address } substitute-as
undo peer { group-name | ipv4-address | ipv6-address } substitute-as
| Parameter | Description | Value |
|---|---|---|
| group-name | Specifies the name of a peer group. | The name is a string of 1 to 47 case-sensitive characters, with spaces not supported. When double quotation marks are used around the string, spaces are allowed in the string. |
| ipv4-address | Specifies the IPv4 address of a peer. | It is in dotted decimal notation. |
| ipv6-address | Specifies the IPv6 address of a peer. | The address is in the format of X:X:X:X:X:X:X:X. |
Usage Scenario
In a BGP/MPLS IP VPN scenario, if the ASs to which two VPN sites belong use private AS numbers, the AS numbers of the two VPN sites may be the same. If a CE in a VPN site sends a VPN route to the connected PE using EBGP and the PE then sends the route to the remote PE, the remote CE will discard the route because the AS number carried by the route is the same as the local AS number. As a result, different sites of the same VPN cannot communicate. The peer substitute-as command can be used on the PE to enable AS number substitution to address this problem. After that, the PE replaces the AS number carried in the VPN route with the local AS number. As a result, the remote CE will not discard the route due to identical AS numbers.
Pre-configuration Tasks
Run the peer as-number command to create a peer or configure an AS number for a specified peer group.