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

[Tim Chown <tjc@ecs.soton.ac.uk>]

On Fri, Mar 09, 2007 at 01:02:00PM -0500, John Spence wrote:
> 
> Comment #1:
> 
> >> How about something like:
> 
> "ULAs are, per the specification, normally /48 prefixes.  Note that a
> larger organization with, for example, a /44 allocation, that wanted to
> be able to map ULAs one-to-one with global prefixes, could generate 16
> ULAs.  These would not summarize, however.  It seems reasonable that the
> organization could also simply generate a /44 ULA, by using fewer than
> 40 bits (36 bits in this example) of the "Global ID" specified in RFC
> 4193."
> 
> Comment #2:
> 
> "Note that scope matching of unicast source and multicast destinations
> is done properly for (now deprecated) site-local addresses, as described
> in RFC 3484.  It is expected that, over time, this feature will also be
> afforded to ULA scope matching.  In the near term, however, implementers
> are cautioned that many deployed devices do not distinguish ULA from
> global-scope addresses, leading to the deployment issue cited above."

Seems reasonable.  For #1 the important aspect is the probability of
clashes should two sites merge.

For #2, our comment was made based on observation of actual behaviour
during experiments.   The issue was fed into the work on 3484 updates
that is collating issues to address.

Tim