Subject: Re: Multiple un-numbered serial links between two routers

From: "Naidu, Venkata" <[email-masked]>
Date: Wed, 16 Apr 2003 11:43:14 -0400

Dennis,

-> What part of RFC 2328 makes section 16.1(2)(b) work better when you
-> have addresses on the p2p links?

  When we make the shortest path tree (actually a directed acyclic
  graph - DAG), we always assume that base OSPFv2 is designed for
  bi-directional links. When we make a graph using the link-state
  database, we must be able to visualize the graph *unambiguously*
  (which half-link from A to B matches to half-link from B to A).
  At least, we can do that using IP addresses with little bit of
  careful subnet addressing.

  RFC 2328 page 166 reads...
        The specification does not require that the above two stage
        method be used to calculate the shortest path tree.  However, if
        another algorithm is used, an identical tree must be produced.
        For this reason, it is important to note that links between
        transit vertices must be bidirectional in order to be included
        in the above tree. ...

  That said, UDLR for OSPF does more than required when OSPF
  runs over unidirectional links.

-> It seems like trying to use addresses
-> to tell you anything more than you would know without the
-> addresses is
-> a mechanism as far outside the protocol as, say, configuring or
-> exchanging the ifindices for unnumbered links would be.

  The *identifiers* between A to B are irrelevant to the discussion
  whether the ids are addresses or ifindices. The only requirement
  is that the "ids" must be unique in the router. W.r.t A and/or B
  (directly connected neighbors) IP addresses and if indices serves
  the same purpose.

  If in GMPLS the exchange of IF_IDs are outside the TE framework,
  I don't think we are able to establish tunnels unambiguously.
  The birectionality test in CSPF is crucial (remember that,
  there is no hello protocol to do the bidirectinality test).

-> Dennis Ferguson

Venkata.

---

From: David Hudek <[email-masked]>
Date: Wed, 16 Apr 2003 22:15:11 -0500

>So the issues and implementation choices are similar for parallel
 >numbered and unnumbered P2P links. Currently, I've implemented a
 >fairly liberal bi-directional check (one back-link will suffice).
 >What is your take on this issue?

Just a quick note that such a liberal approach would seem
to be well supported by Sec 16.1, step 2(b) in its reference
to footnote [23] "...Note that the presence of any link back
to V is sufficient; it need not be the matching half of the
link under consideration from V to W..."

dave hudek
[email-masked]