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

[Acee Lindem <[e-mail]>]

Manohar Naidu Ellanti wrote:
> 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.

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.

>
> Both Cisco and IBM definition cited in the draft don't qualify a router as
> 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
> 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.

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).

>
> -Ellanti
>
>


--
Acee