Subject: Re: [OSPF] External route question

From: "Pat Murphy - (650)329-4044" <[email-masked]>
Date: Mon, 02 Feb 2009 06:34:45 -0700 (PDT)

> 
> Hi Jocke,
> 
> On Feb 1, 2009, at 7:06 PM, Joakim Tjernlund wrote:
> 
> > In RFC 2328, chap 16.4.  Calculating AS external routes, it reads:
> >
> >             If the forwarding address is non-zero, look up the
> >             forwarding address in the routing table.[24] The matching
> >             routing table entry must specify an intra-area or inter- 
> > area
> >             path; if no such path exists, do nothing with the LSA and
> >             consider the next in the list.
> >
> > If I read this literally I should only check that a intra-area or
> > inter-area path exists. I think that the intention is that
> > such a route should be used as forwarding address too, is
> > that right?
> 
> It means that if a forwarding address route exists, it is used for 
> the the next check, (4), in the RC 2328 16.4 external route 
> computation. I believe this is clear if you take the excerpted 
> paragraph in context of section 16.4.

Acee is correct. But note there is a slight omission in this text. The 
forwarding address should not be through a stub area (or NSSA). RFC 3101 
Section 2.5 corrects this omission:

          If the forwarding address is non-zero look up the forwarding
          address in the routing table.  For a Type-5 LSA the matching
          routing table entry must specify an intra-area or inter-area
          path through a Type-5 capable area.  For a Type-7 LSA the
          matching routing table entry must specify an intra-area path
          through the LSA's originating NSSA.  If no such path exists
          then do nothing with this LSA and consider the next in the
          list.

Pat

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From: Joakim Tjernlund <[email-masked]>
Date: Tue, 3 Feb 2009 09:07:50 +0100

>           then do nothing with this LSA and consider the next in the

Thanks, a few questions though:
For Type-5, how do I make sure that the matching route passes through a 
Type-5
capable area?

For Type-7, I guess it is best just to use a route back to the originating 
router?

 Jocke