Subject: ABR questions

From: Chamkaur Dhaliwal <[email-masked]>
Date: Thu, 28 Nov 2002 07:50:11 -0500

Hi,

I have a question about ABR. Suppose you have the following
configuration:

--------------R5----        --------------------
|    AREA 0                                |                     AREA
1                          |
|                                                  |
R6                                     |
|-------------R3-----    ----------------------

Router R5 and R6 are in area 0
Router R6 is in area 1 and is connect to both R3 and R5. That means
there are two ABRs between area 0 and 1.

Next I configure same area ranges on both R5 and R3. That means both R5
and and R3 will generate Type 3 LSA into area 1. How should R6 handle
the both LSAs which advertising the same network.

Thanks.

Regards,

Chamkaur

---

From: "Manral, Vishwas" <[email-masked]>
Date: Thu, 28 Nov 2002 08:18:02 -0500

Hi Chamkaur,

To start off, areas are not configured on a router basis but on a per
interface basis.

If you check sections 16.2 and 16.3 of RFC2328, the issues will become
clearer.

If a router is an ABR, only backbone summary LSA's are examined otherwise
all summary LSA's in the area are examined. Besides only-intra-area routes
are summarized to the area-0, while intra/inter-area routes are advertized
into other areas.

However if we have two LSA's advertizing the same network, check section
16.2 point (7) i.e. the smaller cost is kept.

Thanks,
Vishwas

-----Original Message-----
From: Chamkaur Dhaliwal [mailto:[email-masked]]
Sent: Thursday, November 28, 2002 6:20 PM
To: [email-masked]
Subject: ABR questions

Hi,

Thanks.

Regards,

Chamkaur