Subject: Test for hop-limit in draft-ietf-mpls-rsvp-lsp-fastreroute-02 ?

From: Philip Matthews <[email-masked]>
Date: Thu, 29 May 2003 09:10:17 -0400

I have a question about the test for hop-limit in
the draft-ietf-mpls-rsvp-lsp-fastreroute
that I hope one of the authors will answer.

The draft states (in section 4.1):

       Hop-limit

       The maximum number of extra hops the backup path is allowed
       to take, from current node (a PLR) to a MP, with PLR and MP
       excluded in counting.  For example, hop-limit of 0 means only
       direct links between PLR and MP can be considered.

The word "extra" in the first sentence leads me to believe that the test is:
       (number of hops along backup path from PLR to MP) 
              - (number of hops along protected path from PLR to MP)
       <= hop-limit

However, the example in the second sentence seems to indicate that the
test is:
      (number of hops along the backup path from PLR to MP) - 1
      <= hop-limit

Which test is correct?

Also, I would like to note that, according to the text, the limit applies
to the "backup path". In the Facility Backup method, I assume that what
is really meant is path of the (outer) bypass tunnel, and not the path
of the (inner) backup LSP. Note that the path of the latter might be viewed
as consisting of just a single hop (depending on how you view tunnel hops).

Thanks in advance,

- Philip