Subject: draft-ietf-ipngwg-uni-based-mcast-02.txt

From: Mukul Chawla <[email-masked]>
Date: Fri, 24 Aug 2001 10:32:17 -0700

Im not clear why draft-ietf-ipngwg-uni-based-mcast-02.txt, Section 3
looks _only_ at IPv6 mcast addresses created by mapping 32 bit IEEE 802
MAC addresses (RFC2373, 2.7.2) rather than creating an SSM service range
in IPv6 which uses 112 bit group IDs? What am I missing here? Is there
an IPv6 SSM range which uses 112 bit group IDs?

Thanks,
Mukul

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From: "Brian Haberman" <[email-masked]>
Date: Fri, 24 Aug 2001 13:32:29 -0400

Mukul,
     For the same reason that RFC 2373 only uses the lower 32 bits
for multicast group IDs.  It makes the mapping into IEEE 802 multicast
MAC addresses less likely to lead to collisions.

Regards,
Brian

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From: Mukul Chawla <[email-masked]>
Date: Fri, 24 Aug 2001 11:11:21 -0700

Okay, looks like Im unclear with the basics of IPv6 mcast addresses: I could
use 112 bit group IDs, as long as some mechanism for mapping 112 bit IDs to
ethernet mcast addresses exists, right? Does such a mechanism exist? Is there
an RFC/draft discussing using 112 bit group IDs?

Mukul

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From: "Brian Haberman" <[email-masked]>
Date: Fri, 24 Aug 2001 14:33:21 -0400

Mukul,
     There is no one RFC that discusses IP-layer multicast address
mapping to MAC-layer multicast addresses.  In IPv6, it is covered
in the individual IPv6-over-foo specs.  Take a look at section 7
of RFC 2464.  That shows the mapping of IPv6 multicast addresses to
ethernet multicast addresses.

     Because of this mapping, RFC 2373 discusses only using 32-bit
group IDs for IPv6 multicast addresses.

Regards,
Brian