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

Hi Richard,

   Sorry for the late reply!

Yes, this is a problem with the current spec.  We incorrectly convinced ourselves that such a check is not required.

Here's the proposed change.

We make sure the non-DR router have a synchronized database with the DR before advertising the Type 1 link to other non-DR router.
We declare the DR as a fully synchronized adjacency after having all the DR's LSA request satisfied (i.e., Our LSA update for the LSA requests are acknowledged by the DR.) in addition to having a full adjacency with the DR. 

The rule then will look like the following:  

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

Tanks,

Lili
-----Original Message-----
From: ospf-bounces@ietf.org [mailto:ospf-bounces@ietf.org] On Behalf Of Richard Ogier
Sent: Tuesday, May 17, 2011 12:05 PM
To: ospf@ietf.org
Subject: Re: [OSPF] OSPF Hybrid Broadcast and P2MP Interface Type

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
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