IPv6 End User Assignments

Alan Batie alan.batie at peakinternet.com
Fri May 15 00:04:48 CEST 2009

Steve Bertrand wrote:

> > ... and not enough of the larger (or even small
> > for that matter) *SPs sharing information as to what is currently
> > working for them, and what is not working for them.

FWIW, this is what we're (a small regional ISP) starting to set up and
the thoughts behind it...

> > I don't like /64 where only one subnet is needed, because I've made that
> > mistake before. Inevitably, the site will need more space (says Murphy).
> > I do like /56 for all, unless a /48 can be forseen by yourself as the
> > network op, or warranted immediately by the client.

My feeling is yes /64 is a mistake, but likewise, /48 seems way overkill
for the vast majority of customers.  We have 2607:f678::0/32, which I've
start allocating out (to willing guinea pigs, we're still in the process
of connecting up) with 2607:f678:1::0/36 for our dsl block, with a
default allocation of /60, but with allocations starting from the left,
as I've seen recommended elsewhere, and which I'm pretty sure is SOP:

2607:f678:10::0/60 Cust 1
          11::0/60 Cust 2

By growing from the left, if any customer needs a larger space, all we
have to do is change the prefix length.  By the time the two ends come
anywhere near meeting (if they ever do), we'll have enough experience to
decide how to handle it.

The main point is that it is easier to shorten a prefix than to lengthen
it, as the latter runs the risk of having to remove service (almost
guaranteed, as customers are likely to follow the left to right
allocation practice as well).  Thus, it seems logical to be conservative
(for a somewhat liberal definition of "conservative") in the initial
allocations since it's nearly trivial to expand them.

Being a small regional provider, we don't have many large enterprise
customers, but for that class, I'd probably break out a separate block,
say 2607:f678:2::0/36 which is allocated similarly but defaulting to /48
to keep from complicating the "small user" space.

The main issue is deciding how wide to spread the "top" --- if it's too
wide, we could fragment our space and some future change in the business
 cause us to have to intermix (e.g. some dsl, some colo), but there's so
much room, it's hard to see that happening: there's still 13 /36's left
in the block to accomodate future needs (using a whole /36 for our
internal use).

If we limit the "small user" space to /56's, that gives us 1M small
users; likewise, the "large user" space gives us 64K /48's (and I can't
see any of them needing more, for most /56 is probably plenty), way more
than we'll ever have in our wildest dreams...

On the other hand, 64K /48's *would* cover our entire customer base
several times over, but it just seems hideously wasteful.  That might
argue for not bothering with the separate "large user" space, but it
just seems administratively cleaner.

More information about the ipv6-ops mailing list