Subject: [Isis-wg] an ISIS question

From: "He, James" <[email-masked]>
Date: Wed, 1 Dec 1999 08:54:11 -0500

I am thinking about a scenario like this: three ISIS systems R1, R2, and R3.
R1 is a L1/L2 system with area addresses 1 and 2. R2 is a L1-only system
with
an area address of 1. R3 is also a L1-only system with an area address of 2.
All three systems are connected via a LAN. Obviously the systems will
establish
L1 adjacencies to each other.

Q:  R1 will have L1 adjacencies to R2 and R3. However, R2 and R3 will not
be adjacent to each other as the two systems do not a common area address.
Will R1 have two L1 link state databases as we have two L1 areas bridged 
by R1?  Normally different L1 areas are connected via different L1/L2
systems.
So we are looking at a degenerated case.

Thanks.

James

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From: Mike Shand <[email-masked]>
Date: Wed, 01 Dec 1999 14:42:26 +0000

>by R1?  Normally different L1 areas are connected via different L1/L2

No. All the systems will reside in the area with area addresses 1 & 2. You 
are correct that the adjacency between R2 and R3 will not come up and in 
any sensible implementation it will complain about an area mismatch.

>So we are looking at a degenerated case.

Yes, this is not a recommended configuration. In general you should always 
configure all systems on the LAN to have the same set of area addresses. 
The only exception to this is in the dynamic case where you are trying to 
add/remove/change an area address.

         Mike