Subject: draft-ietf-ipngwg-uni-based-mcast-03.txt

From: Thomas Narten <[email-masked]>
Date: Thu, 27 Sep 2001 10:43:45 -0400

I have  question about the references to SSM. In particular, the
document says:

>    The unicast prefix-based IPv6 multicast address format supports 
>    Source-specific multicast addresses, as defined by [SSM ARCH].  To 
>    accomplish is, a node MUST: 
>     
>            o Set P = 1. 
>            o Set plen = 0. 
>            o Set network prefix = 0. 
>     
>    These settings indicate that the multicast address is being used in 
>    source-specific multicast transmission.  The source address field in 
>    the IPv6 header identifies the owner of the multicast address. 

Is it required (or desirable) for the network prefix to be set to 0 as
stated above? I.e., the test for the address being SSM would be
something like:

           - SSM - All IPv6 SSM multicast addresses will have the
              format FF3x::/96.

In a previous discussion, I believe someone asserted that even for SSM
addresses, having the identity of the sender embedded within the
address could be useful. I.e, putting in the link value rather than
zero could help debugging.

What are the pros and cons of doing this? I worry that this document
seems to be putting constraints on the format of SSM addresses, when
in fact the SSM document to which it refers does not seem to be
finished yet (e.g., it does not seem to be in sync with the documents
being discussed here).

>    [SSM ARCH] H. Holbrook and B. Cain, "Source-Specific Multicast 
>               for IP", Work In Progress, March 2001. 

(which I assume is draft-holbrook-ssm-arch-02.txt)

Indeed, shouldn't this reference be considered normative? What is the
current status of the ssm-arch document?

Thomas