Re: I-D ACTION:draft-ietf-v6ops-addcon-00.txt

[Mark Smith <ipng@69706e6720323030352d30312d31340a.nosense.org>]

Hi,

On Tue, 13 Jun 2006 09:25:00 +0200
Brian E Carpenter <brc@zurich.ibm.com> wrote:

> Just a few comments on this:
> 

<snip>

> > 2.4.  Network Level Design Considerations
> 
> I suggest adding a bullet at the end of this section along these
> lines:
> 
> o It is possible that as registry policies evolve, a small site
>    may experience an increase in prefix length when renumbering,
>    e.g. from /48 to /56. For this reason, the best practice is
>    number subnets compactly rather than sparsely, and to
>    use low-order bits as much as possible when numbering subnets.
>    In other words, even if a /48 is allocated, act as though
>    only a /56 is available. Clearly, this advice does not apply
>    to large sites and enterprises that have an intrinsic need
>    for a /48 prefix.
> 

Other than knowing it has been going on, I'm not up to date with what
has been discussed regarding this policy change. 

From the brief info I read a while back, the proposal was two sizes of
allocations, /48s or /56s. Has that changed at all to being a varying
prefix value between /48 and /56 ?

In either case, I'm wondering if there are methods of address
management from the ISP side of things to allow for smaller customers
who might exceed a /56 allocation. For example, very quickly off of the
top of my head, one way an ISP could handle this would be allocate each
small customer a /48, but only assign them the first /56 out of it. If
the customer needs more address space they then get the full /48 that
was pre-allocated for them. Of course, that means the ISP may end up
effectively running out of address space before much of it has actually
been used. At that point the ISP could then start allocating
further /56s out of the previously allocated /48s (best out of only one
of them until it is used up I'm sure), although the problem of course
is out of which customers allocated /48 to the new /56s come from. If
the allocations sizes are fixed at /48 and /56, I suppose if the
customer who's previous /48 the new, different customer's /56 was
allocated does exceed their original /56, then they could renumber to a
new /48 allocation. At least then their addressing would have been stable
for quite a while. Maybe if the new /56 was allocated out of the first
ever allocated /48, then it is fairly likely the first customer will
probably never grow beyond their original /56 assignment, as I'd guess
there would have been quite a length of time from between the first /48
allocation and the last.

Anyway, I haven't put much thought into it, so there may be far better
ways to deal with the ISP side of the /48, /56 policy change. I think
it would be good to cover any methods of dealing with it in this draft
if possible.

Regards,
Mark.