RE: OSPF inter-AS extensions for GMPLS (RFC5392) questions

"Fabien Verhaeghe" <fabien.verhaeghe@marben-products.com> Mon, 09 March 2009 07:39 UTC

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From: "Fabien Verhaeghe" <fabien.verhaeghe@marben-products.com>
To: "'Adrian Farrel'" <adrian@olddog.co.uk>, <ccamp@ops.ietf.org>
Subject: RE: OSPF inter-AS extensions for GMPLS (RFC5392) questions
Date: Mon, 9 Mar 2009 08:39:20 +0100
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Hi Adrian,

See in-line

> Hi Fabien,
> 
> > Sorry to come a little late on this but I have a question on inter-AS
> > extensions RFC5392 (also applicable on ISIS extensions).
> > In section 4:
> > " Only some essential TE information for the link needs to be
> >   advertised; i.e., the Link Type, the Remote AS number, and the Remote
> >   ASBR ID."
> >
> > First what does "remote" mean here? is it remote in the context of the
> > proxied link or in the context of the Router?
> > i.e.
> >
> > RouterA in AS1 ------TE Link------ RouterB in AS2
> >
> > I guess it is in the context of the link. That is in LSA generated by
> > router
> > A for B->A link (proxied) we put AS1 and routerA ASBR Id. Is that
> correct?
> 
> Yeah, you could say "in the context of the router." Or even "in the
> context
> of the IGP instance". Since the IGP will only be running in one AS, the
> advertising router is talking about the IDs of the "other" AS and ASBR.
> 

Sorry but I am still a little bit confused.
Router A generates 2 LSAs for a TE link between A and B.
One for A->B direction and one for B->A direction (because B is in a
separate IGP).
Are you saying that in both LSAs the remote AS number sub TLV is set to
Router A's AS?

If yes what I don't get is how other routers in this AS knows which LSA
corresponds to A->B direction and which one corresponds to B->A direction.

That is why I thought "remote" in the text mentioned in my first email
refers to the "link context". Then both LSAs would contain different remote
AS/ASBRId so that we can tell which one corresponds to each direction.

Please let me know if I miss something...

Thanks
Fabien