Subject: OSPF/Unnumbered

From: Fabien Verhaeghe <[email-masked]>
Date: Fri, 8 Oct 2004 08:15:11 +0200

Hi,

RFC2328 section 12.4.1.1 describing how to encode P2P link into a router LSA required to set the
MIB-II
interface index in case of unnumbered interface.
But there is no mean for other router receiving the LSA to guess if a P2P link is unnumbered or not.

This may be a problem when a virtual link path is terminated on such an unnumbered interface.
As explained in section 15 this will prevent such virtual link to be up. Indeed on virtual link, the
Hello packet
are monocasted to the IP address found in the router LSA link that point back to the virtual link.
If it is
an unnumbered interface the router will eventually send Hello using the MIB-II If index as
destination IP address.

Isn't it better to encode a valid router IP address instead of the MIB-II index in the router LSA
type 1 link
when describing unnumbered interface?
Do you see any interop problem?

Regards,
Fabien

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From: Acee Lindem <[email-masked]>
Date: Fri, 8 Oct 2004 08:55:26 -0400

Hi Fabien,

While this solution would simplify the virtual link neighbor address selection,
I don't think we should change the LSA link format at this time. Many
implementations use a heuristic of determining whether the best path
link data is a valid IP address and, if not, searching the virtual link
endpoint router's backbone router LSA for a routable address. You
can look at an example of this in John Moy's GPL ospf
implementation (www.ospf.org).

Hope this helps,
Acee