Subject: Seeming contradiction on forwarding addresses?

From: Mike Fox <[email-masked]>
Date: Mon, 13 Oct 2003 17:32:36 -0400

RFC 2328 says, in section 12.4.4.1 regarding forwarding addresses in
external LSAs:

> Note that when the forwarding address field is non-
> zero, it should point to a router belonging to
> another Autonomous System.

But then when discussing calculation of external routes in section  16.4 it
says:

> 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.

So the RFC says that a forwarding address should be to an AS external
address, but no one can use an external LSA if the only way to reach the
forwarding address is via an AS External route?  Footnote 24 re-emphasizes
that point also.  Is there something I am missing here?

Mike
-----------------------------------------------------------------------
Enterprise Network Solutions
-----------------------------------------------------------------------
Research Triangle Park, NC  USA

---

From: Acee Lindem <[email-masked]>
Date: Mon, 13 Oct 2003 17:53:14 -0400

Hi Mike,

>that point also.  Is there something I am missing here?
The  thing here is that the forwarding address is for a router that
provides a path to IPv4 prefixes
outside the OSPF routing domain. However, the forwarding address itself
must be reachable
by an OSPF intra-area or inter-area route (which is by definition part
of the OSPF routing
domain).  In this context, I prefer to use the term OSPF routing domain
rather than AS since
there will often be non-OSPF routes in use within an AS running OSPF as
the IGP.

I hope I've made sense.

Acee