Subject: Re: area-border router's behaviour

From: "Liu B." <[email-masked]>
Date: Wed, 23 Oct 2002 13:26:03 +0100

Hi,

I have a further question ... define the areas vs. choose ABR, which one
goes firstly?

Thanks

Bin

-----Original Message-----
From: Kostiner, Assaf (Assaf) [mailto:[email-masked]]
Sent: Wednesday, October 23, 2002 8:30 AM
To: [email-masked]
Subject: area-border router's behaviour

Hi,

There are couple of issues i can't understand:

1. In RFC an area-border router (ABR) is defined as one that is attached to
multiple areas, while Cisco and IBM defined later ABR as one that is
physically or virtually connected to the backbone. I understand theire
reason for changing the RFC definition. What i don't understand, is why does
the RFC allows a router which is connected for example only to areas 1 and
2, to be an ABR, and to advertise summaries from one to the other. This
router is allowed to use only summaries received from area 0, when running
SPF, so what's the point?

2. Overlapping area ranges - in RFC 1583, an ABR which aggregates all
subnets of 10.0.0.0/8 ignores summaries which fall into this range, like
8.3.0.0/16. That's why, any such subnet outside the aggregated area will
become unreachable. Why does the ABR ignores all such summaries. If it
didn't ignore them, all subnets could be reachable...

I would appreciate any help, Assaf.