Subject: about Area Splitting

From: "Li, Ke Qin (Peter)" <[email-masked]>
Date: Tue, 9 Dec 2003 09:30:10 +0800

Hi,

        I've read the Internet Draft "OSPF Areas Considered Harmful" written
by Mikkel Thorup
http://www.ietf.org/internet-drafts/draft-thorup-ospf-harmful-00.txt. In
Section 8.0 "Summarization and infinite loops", a scenario is described
where area splitting results in infinite routing loop (although IMHO it is
black hole). I think it is a basic problem related to OSPF hierarchy and
area range. Has this problem been discussed in this list before? If yes,
what is the solution?

        Thank you very much!

Keqin Li
Bell Labs Research China
Tel: 86-10-68748088-8438

---

From: Sina Mirtorabi <[email-masked]>
Date: Mon, 8 Dec 2003 18:12:30 -0800

Keqin,

Tunnel adjacency allows to both avoid suboptimal routing ( because of
intra-area path preference ) and automatic partition repair when the
area is partitioned and summarization is performed

http://www.ietf.org/internet-drafts/draft-mirtorabi-ospf-tunnel-adjacenc
y-00.txt

There were some concerns regarding the recursive TA and a new version of
the document ( available soon) will prevent recursive TA

Thanks
Sina

->-----Original Message-----
->From: Mailing List [mailto:[email-masked]] On
->Behalf Of Li, Ke Qin (Peter)
->Sent: Monday, December 08, 2003 5:30 PM
->To: [email-masked]
->Subject: about Area Splitting
->
->
->Hi,
->
->        I've read the Internet Draft "OSPF Areas Considered
->Harmful" written by Mikkel Thorup
->http://www.ietf.org/internet-drafts/draft-thorup-ospf-harmful-
00.txt. In Section 8.0 "Summarization and infinite loops", a scenario is
described where area splitting results in infinite routing loop
(although IMHO it is black hole). I think it is a basic problem related
to OSPF hierarchy and area range. Has this problem been discussed in
this list before? If yes, what is the solution?

        Thank you very much!

Keqin Li
Bell Labs Research China
Tel: 86-10-68748088-8438

---

From: Acee Lindem <[email-masked]>
Date: Mon, 8 Dec 2003 21:38:26 -0500

Li, Ke Qin (Peter) wrote:

>black hole).
Hi Kegin,

The traffic should result in an ICMP reject since any deployable
implementation will install a reject route corresponding
to its active area ranges that do not coincide with computed intra-area
routes. RFC 2328 doesn't state this explicitly but
it is implied by section 3.5 (it says a single route may be advertised
for an area range - this implies a route exists).

>I think it is a basic problem related to OSPF hierarchy and
I'm not sure how serious the problem is since there haven't been that
many complaints. However, as
Sina points out, the proposed Tunnel Adjacency (TA) extension can be
used to repair a partitioned
non-backbone area.

---

From: Tony Przygienda <[email-masked]>
Date: Tue, 9 Dec 2003 13:30:15 +0100

>area range. Has this problem been discussed in this list before? If yes,
I discussed and started to write once with John what we considered the
optimal solution (and I know some people
implemented it). Basically, when you realized that you see through the
backbone advertisement of an ABR in your
area that you
don't have intra-area connectivity to, you inject with the summary all
the more specifics into the backbone. Simple
to implement, the only real disadvantage really being that you may put
tons of routes into the backbone. On the other
hand, you're only real other solutions are either for one to stop
advertising (avg. 50% of area goes down) or
maybe have some complicated 'tunnel-through-backbone' solution, which we
didn't think was worth the effort.

If anybody feels like writing that down, I can help a bit, I don't think
I will find my writedown anymore on all my
harddisks lying around ; -)

-- tony