I’ve always thought that Cisco introduced the BGP Local-AS feature into IOS to support complex MPLS VPN design scenarios. Obviously I was wrong, the early documentation always describes an ISP AS merging scenario. Unfortunately, all the articles I’ve found skip some important details: they describe the basics and the configuration commands, but forget to mention the impact on the AS paths received by the ISP customers. Obviously we need a more thorough description of this feature.
Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.