Subject: [Isis-wg] Sys-ID Length - FINAL Round

From: Jeff Parker <[email-masked]>
Date: Mon, 8 Apr 2002 14:53:24 -0400

- Motivation for length of 6
- Note that some TLVs assumer length of 6

- The range (1..8) is not discussed.  I'm happy to, but don't see the point.

- jdp

6.0 Variables Which Are Constant

   Some parameters to the protocol were defined as variable, but rarely
   vary in practice.  These include

(1)  System-ID Length

(2)  Maximum Area Addresses

6.1 System-ID Length

   The System ID is allowed to be as long as 8 bytes.  Since it was easy
   to use an Ethernet MAC address to generate a unique 6 byte System ID,
   and since the SystemID only has significance within the IGP Domain, 6
   bytes has proved to be ample and is widely used. Moreover, new IS-IS
   TLVs such as the Traffic Engineering TLVs, are assuming a 6 byte Sys-
   tem ID, so choices other than 6 are difficult to support.

   Implementations may interoperate without being able to deal with Sys-
   tem IDs of any length other than 6. Of course implementation must
   check the ID Length defined in the IS-IS PDUs it receives, and dis-
   card PDUs that do not match the local value.  But a System ID of
   length 6 is so widely used that this is the only value an implementa-
   tion needs to support.

- jeff parker
- axiowave networks
- Times are bad. Children no longer obey their parents, and everyone is
writing a book
- Cicero (106-43 BCE)
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From: Neal Castagnoli <[email-masked]>
Date: Mon, 8 Apr 2002 15:11:29 -0700

I think that 0 is also a valid value for systemID, and is equivalent to six,
similar to the 0/3 maximum area addresses.

  --Neal