Subject: draft-ietf-ospf-abr-alt-04.txt

From: Manohar Naidu Ellanti <[email-masked]>
Date: Thu, 11 Apr 2002 12:22:18 -0400

Is it possible that a router which is attached to multiple areas but not
attached to area 0, can still be an ABR?

For isntance, if a R1 has area 1,2 and 3 . Can it advertise summary-lsa for
area 1 into 2 and 3 ? and similarly summary-lsa for 2 into 1 &3 etc.

Both Cisco and IBM definition cited in the draft don't qualify a router as
ABR unless it is attached to backbone. But isn't that restrictive if one
knows that there is no real area 0 for some applications? Even if one were
to have area 0, in the above example  R1 might have an additional interface
that is not connected to anything but configured with area id 0.0.0.0. The
router may not have any adjacency over the backbone as there is no other
router.

-Ellanti

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From: Acee Lindem <[email-masked]>
Date: Thu, 11 Apr 2002 15:25:04 -0400

> area 1 into 2 and 3 ? and similarly summary-lsa for 2 into 1 &3 etc.

RFC 2328 defines an ABR as a router that is attached to two or more areas.
By attached, it means it has at least one OSPF interface in the area in
UP state.

> ABR unless it is attached to backbone.

Not exactly - anyway this why it is titled *alternate* ABR behavior.

> But isn't that restrictive if one
> knows that there is no real area 0 for some applications?

If you have multiple areas, your network should contain a backbone.

> Even if one were

This really isn't a valid network design - unless of course you're connecting
to a BGP/MPLS VPN backbone (but that's a whole different story).

--
Acee