Subject: question on rfc2547bis re inter-AS

From: Mark Duffy <[email-masked]>
Date: Wed, 12 May 2004 18:05:46 -0400

Hi this is a question for the authors of rfc2547bis regarding section 10 
Multi-AS Backbones.

In the approach "b) EBGP redistribution of labeled VPN-IPv4 routes from AS 
to neighboring AS":

               ... The ASBR then uses EBGP to redistribute those labeled
          VPN-IPv4 routes to an ASBR in another AS, which in turn
          distributes them to the PE routers in that AS, or perhaps to
          another ASBR which in turn distributes them ...

Is it the case that the ASBRs (one or both at each ebgp peering) replace 
the BGP next hop in the VPN-IPv4 routes with their own address?  And 
therefore they also assign a label to the VPN-IPv4 route and perform label 
switching on the "inner" (vpn) label while forwarding vpn packets?

The document doesn't state that but it would seem to follow from the normal 
bgp behavior of updating the next hop.  It would also explain why this 
section b) does not contain all the same discussion as section c) regarding 
the establishment of an "outer" LSP from ingress PE to egress PE.

Although for some reason section b) does say:

          This procedure requires that there be a label switched path
          leading from a packet's ingress PE to its egress PE.

Is that perhaps referring to the LSP represented by the inner (vpn) 
labels?  Because if the ASBRs are really switching on the vpn label, then 
there is not an outer LSP from ingress PE to egress PE.  Rather there is an 
outer LSP from ingress PE to ASBR, perhaps another outer LSP from ASBR to 
ASBR, and an outer LSP from ASBR to egress PE.

Thanks, Mark