Subject: [mpls] One LDP Implementation specific question of receive label mapping for prefix FECs

From: "Dutta, Pranjal" <[email-masked]>
Date: Sun, 9 Apr 2006 01:40:40 +0530

Hi,

               I have a basic confusion on the "Label Mapping Receive
Procedure" explained in the appendix of RFC 3036. One step says "Find
the FEC next hop". When Ru receives a label mapping for a FEC of type
IPv4/v6 prefix from Rd, the next hop for the FEC can be determined after
route lookup. Now here, for looking up the FEC at Ru do we need to do
exact match or Longest prefix match? It is quite possible that the
prefix as FEC mapped by Rd may be within a supernetted  prefix at Ru.
The reason why I am asking is I guess the implications could be
different based on whether LSR is merge capable or non-merge capable.

Thanks in advance,

Pranjal

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From: Eric Rosen <[email-masked]>
Date: Mon, 10 Apr 2006 14:09:11 -0400

> When Ru receives a label mapping for a FEC of type IPv4/v6 prefix from Rd,
> the next hop  for the FEC can be determined after  route lookup. Now here,
> for looking  up the  FEC at Ru  do we  need to do  exact match  or Longest
> prefix match? It is quite possible that the prefix as FEC mapped by Rd may
> be within a supernetted prefix at Ru. 

It's a  little hard  to understand what  you're asking.  By  definition, one
cannot change the FEC in mid-LSP.  If  the FEC is an address prefix, and you
reach a  point where that address prefix  is not in the  routing table, then
the LSP terminates.