draft-ietf-v6ops-addcon-03.txt ... ULAs of shorter-than-/48 and ULA multicast scope matching ...

["John Spence" <spence@commandinformation.com>]

Hello Gunter, et. al.;  two comments:

1) Section 2.2, regarding ULAs, they are indeed defined as /48.  I
suggested to the ULA RFC writers that the length be relaxed, allowing
for ULAs of any prefix length, such that an organization that had, say,
a /44 routable could also generate a /44 ULA.  The only impact would be
to increase the odds of collisions later if two organizations merged.
The writing team decided not to put that into the RFC, but did say on
the mailing list that since ULAs are internal, there is nothing to stop
an organization from doing just that.

Perhaps in the addconn draft we might make a statement to the effect
that an organization could choose to self-allocate a shorter-than-/48
ULA to match a shorter-than-/48 global allocation, if they chose,
subject to the caution on collisions noted above.

We did discuss this back in March 2006
(http://psg.com/lists/v6ops/v6ops.2006/msg00137.html), and thought
perhaps a note in the text would be appropriate as background, but leave
the emphasis on /48 since that is "per spec".  Just wanted to mention it
again to make sure it was not lost.

2) also Section 2.2, regarding multicast, the text states that:

"As an example of the problems ULAs may cause, when using IPv6 multicast
within the network, the IPv6 default address selection algorithm prefers
the ULA address as the source address for the IPv6 multicast streams. "

Looking at RFC 3484, it says:

"We map unicast link-local to multicast link-local, unicast site-local
to multicast site- local, and unicast global scope to multicast global
scope.  For example, unicast site-local is equal to multicast
site-local, which is smaller than multicast organization-local, which is
smaller than unicast global, which is equal to multicast global."

The RFC does not mention ULA because ULA definition came later, and
site-locals were deprecated.  I would expect that an update of 3484
would apply the same logic for ULA, and, hopefully, implementers today
are implementing scope matching based on ULAs.

Is there another reference that states that ULA unicast source is always
preferred for multicast addresses, where the sending interface has both
ULA and global unicast addresses?

John Spence