Subject: RE: get rid of IPv4 compatibles?

From: "Dave Thaler" <[email-masked]>
Date: Tue, 19 Mar 2002 22:36:39 -0800

Antonio Querubin writes:
> If it is how about just defining mapped multicast addresses already?
[...]
>    |                80 bits               | 16 |      32 bits        |
>    +--------------------------------------+--------------------------+
>    |0000..............................0000|FFFF|IPv4 multicast group |
>    +--------------------------------------+----+---------------------+

This has been discussed before, and the above format is illegal, since
all multicast addresses must begin with 0xFF, not 0x00.

I think someone did once propose a format which was out of the legal
multicast space.

-Dave
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From: Antonio Querubin <[email-masked]>
Date: Tue, 19 Mar 2002 22:08:45 -1000 (HST)

> all multicast addresses must begin with 0xFF, not 0x00.

You mean all IPv6 multicast addresses?  But here we mean mapped
representations of IPv4 addresses which in this case happen to be
multicast.  For implementation purposes I think it would be simpler to
keep the /96 prefix identical for both IPv4 unicast and IPv4 multicast
addresses.  Otherwise, tests for address type become a little more
complicated since we'd be adding yet another prefix to test for and
another map classification.

---

From: Brian Haberman <[email-masked]>
Date: Wed, 20 Mar 2002 10:15:21 -0500

> I think someone did once propose a format which was out of the legal

And one of the biggest issues we had with that proposal was that there
was no easy way to map an IPv4 scoped multicast address into a
corresponding IPv6 scoped multicast address.

Brian