Subject: Re: [Isis-wg] Re: internet-drafts/draft-ietf-isis-wg-255adj-02.txt

From: [email-masked] (Christian E. Hopps)
Date: 15 Nov 1999 04:05:45 -0500

Radia Perlman - Boston Center for Networking <[email-masked]> writes:

> It is possible to be DIS on more than 255 LANs provided that a 7-byte
> pseudonode ID, unique in the area, can be selected. The IS-IS
> specification states that the DIS's system ID is the first 6 bytes of
> the pseudonode ID. However, the only property of the 7-byte Pnode ID
> necessary for correct operation of the routing algorithm is that
> the 7-byte ID be unique in the area.

A couple small points:

There are specific checks against the system ID when processing a
received LSP (to determine if its self-originated).  So your proposed
text should probably point out that these need to be expanded to check
against any possible value that might be generated for the 6-byte
prefix.

It seems to me that there is nothing in the standard that requires
System ID's to be MAC addresses.  Therefore how can you know that
another system's System ID won't be one of your MAC addresses?  At least 
2 implementations I know of let the user set the system ID to whatever
they choose.  (And yes, I do think this would be rare in any case).

Again these are small points. I like the idea of using MAC addresses.  I
think the first case can be handled with some additional text. The
second case can probably be handled by requiring a run-time
configuration variable.  That way if, for some bizarre reason, there is a
namespace collision at least the user asked for it :)

Chris.

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From: Tony Li <[email-masked]>
Date: Wed, 17 Nov 1999 14:47:44 -0800

|  It seems to me that there is nothing in the standard that requires
|  System ID's to be MAC addresses.  Therefore how can you know that
|  another system's System ID won't be one of your MAC addresses?  At least 
|  2 implementations I know of let the user set the system ID to whatever
|  they choose.  (And yes, I do think this would be rare in any case).

The spec requires that the manager insure that the system id is unique
within a L1 area for L1 systems and unique within L2 for L2 systems.
Frankly, I think that this is overly liberal and the sysadmin should simply
insure uniqueness domain-wide.

You are correct.  Mapping the MAC address is convenient, but is not a
requirement.

Tony