Subject: I/F ID uniqueness and rfc2462bis

From: Derek Smalls <[email-masked]>
Date: Wed, 1 Jun 2005 16:11:22 -0700 (PDT)

There seems to be a slight inconsistency in rfc2462bis
regarding the uniqueness of interface identifiers on
an interface. 

>From Section 5.4:
" .. new types of addresses have been introduced where
the interface identifiers are not necessarily the same
for all unicast addresses on a single interface
[RFC3041] [RFC3972]. " 

However, clause d) in Section 5.5.3 makes references
to "link's interface identifier" and seems to assume
that a given IPv6 interface has a single interface
identifier. Will this algorithm work if there are
multiple interface identifiers on a given interface?

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Fri, 03 Jun 2005 04:06:36 +0900

>>>>> On Wed, 1 Jun 2005 16:11:22 -0700 (PDT), 
>>>>> Derek Smalls <[email-masked]> said:

> multiple interface identifiers on a given interface?

The short answer is YES.

As you used the word "slight", I'm not sure if this requires a change
to the rfc2462bis text, but I don't mind revising Section 5.5.3 to,
e.g.:

    d) If the prefix advertised does not match the prefix of an address
       already in the list, and the Valid Lifetime is not 0, form an
       address (and add it to the list) by combining the advertised
       prefix with an interface identifier of the link as follows:

People may still wonder what the host should do if there are multiple
interface identifiers, and they might think rfc2462bis should clearly
specify the behavior.  However, I personally think it's overkilling
for rfc2462bis.  After all, the most typical case is that the host
uses the single interface identifier derived from the interface's
link-layer address.  And the specifications using additional
identifiers ([RFC3041] or [RFC3972]) describes how to form addresses
with the additional identifiers inside the specific documents.

Summarizing the above, I see three options:

1. just leave the current text as is. (since the "issue" is very
   minor)
2. introduce a minor modification, replacing "the interface
   identifier" with "an interface identifier" wherever appropriate.
3. in addition to option 2, add detailed description about how the
   host should do if it has multiple interface identifiers

I can live with either 1 or 2, but I think option 3 is overkilling.

Opinions?

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]

---

From: Derek Smalls <[email-masked]>
Date: Thu, 2 Jun 2005 21:24:31 -0700 (PDT)

I think option 2 is the best. The standards the way
they are today are quite vague on the uniqueness of
interfaces IDs on an interface, uniqueness of
advertised prefixes across multiple links etc. It's
best to reduce ambiguity as much as possible.

--- JINMEI Tatuya / 神明達哉

		
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