Subject: LL3, LL21 and potential new issue

From: "Philip Nye" <[email-masked]>
Date: Wed, 5 Mar 2003 10:10:55 -0000

One thing that has become clear in discussions of TTL is that Multicast
packets are potentially subject to different conditions from unicast in that
the sender has no direct control over whether they are routed. This makes
arguments for setting TTL=1 stronger for Multicast packets and potentially
different rules should apply for multicast.

However, there could be other ways around this issue: We could disallow or
discourage packets with a LL source address being sent to any multicast
destination address outside the 224.0.0/24 link-local scoped multicast
prefix. This would seem very much in keeping with the principle of LL.

I have been unable in a quick search to find the RFC which defines this
scope however it is mentioned in rfc2365 and elsewhere.

Philip

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From: Stuart Cheshire <[email-masked]>
Date: Wed, 12 Mar 2003 23:20:41 -0800

Philip Nye wrote:

>However, there could be other ways around this issue: We could disallow
>or discourage packets with a LL source address being sent to any multicast

Nice idea, but there *aren't* any SSM multicast addresses in the 
224.0.0/24 prefix. There *aren't* any dynamically assigned multicast 
addresses in the 224.0.0/24 prefix.

This restriction effectively says that LL hosts can't use multicast, 
except for a few IANA-assigned well-known addresses in 224.0.0/24.

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer, Inc.
 * www.stuartcheshire.org