SimpleASFilter is a BGPRouteFilter that drops routes that have a particular AS in their AS path. This is typically used in loop prevention, where an inbound filter from an EBGP peer drops routes that contain our own AS number
This works on both regular EBGP and CONFEDERATION EBGP sessions
| SimpleASFilter (const AsNum &as_num)
|bool filter (InternalMessage<A>& rtmsg)
Reimplemented from BGPRouteFilter.