Can there be two or more Autonomous Systems within the same MPLS domain?
This is possible only under very restricted circumstances. Consider the ASBRs of two adjacent ASes. If either or both ASBRs summarize eBGP routes before distributing them into their IGP, or if there is any other set-up where the IGP routes cover a set of FECs which differs from that of the eBGP routes (and this would almost always be the case), then the ASBRs cannot forward traffic based on the top-level label. A similar argument applies to TE tunnels. Some traffic usually will be either IP forwarded by the ASBR, or forwarded based on a non-top-level label.
