Subject: Re: [OSPF] OSPF Hybrid Broadcast and P2MP Interface Type

From: Richard Ogier <[email-masked]>
Date: Tue, 17 May 2011 09:04:39 -0700

Section 3.6 of draft-nsheth-ospf-hybrid-bcast-and-p2mp-01
has the following rule:

o  If a router is not the DR and has a full adjacency to the DR, it
   MUST add a Type 1 link corresponding to each neighbor that is in
   state 2-Way or higher.

Suppose i and j are non-DR routers.  It seems to me that i should
also require that the DR's router-LSA include a link to j before
i adds a Type 1 link corresponding to j, in order to ensure that
i and j are fully synchronized before either uses the other as
a next hop.  Is there a reason why this condition was omitted?

To explain further, the SPT calculation (Section 16.1 of RFC 2328)
requires that router j advertise a link back to router i before i
can use j as a next hop (and vice versa). Thus, routers i and j can use
each other as a next hop if they both advertise a link to each other.

Therefore, the above rule from draft-nsheth only ensures that
routers i and j are fully adjacent with the DR before either can
use the other as a next hop.  As a result, the DR might not be fully
adjacent with router i or j, and thus i and j may not be fully
synchronized.  Note that full adjacency with a neighbor does not
imply that the link state databases are synchronized (see footnote 23
in RFC 2328).  It only means that the router is at least as
up-to-date as the neighbor, since it only means that all Link
State Requests have been satisfied.

Please correct me if I am mistaken.

Richard