IPv6 Default Allocation - What size allocation are you giving out

Royce Williams royce at techsolvency.com
Thu Oct 9 04:14:51 UTC 2014


On Wed, Oct 8, 2014 at 8:07 PM, Faisal Imtiaz <faisal at snappytelecom.net>
wrote:

> Like I said, this was my understanding.... I am glad that it is being
> pointed out to be in-correct....
>
> I don't have a reason for why a /64 as much as I also don't have any
> reason Why NOT....
>
> So, let me ask the question in a different manner...
> What is the wisdom / reasoning behind needing to give a /56 to a
> Residential customer (vs a /64).
>

Quoting RFC6177 (successor to RFC3177):

   While the /48 recommendation does simplify address space management
   for end sites, it has also been widely criticized as being wasteful.
   For example, a large business (which may have thousands of employees)
   would, by default, receive the same amount of address space as a home
   user, who today typically has a single (or small number of) LAN and a
   small number of devices (dozens or less).  While it seems likely that
   the size of a typical home network will grow over the next few
   decades, it is hard to argue that home sites will make use of 65K
   subnets within the foreseeable future.  At the same time, it might be
   tempting to give home sites a single /64, since that is already
   significantly more address space compared with today's IPv4 practice.
   However, this precludes the expectation that even home sites will
   grow to support multiple subnets going forward.  Hence, it is
   strongly intended that even home sites be given multiple subnets
   worth of space, by default.  Hence, this document still recommends
   giving home sites significantly more than a single /64, but does not
   recommend that every home site be given a /48 either.

   A change in policy (such as above) would have a significant impact on
   address consumption projections and the expected longevity for IPv6.
   For example, changing the default assignment from a /48 to /56 (for
   the vast majority of end sites, e.g., home sites) would result in a
   savings of up to 8 bits, reducing the "total projected address
   consumption" by (up to) 8 bits or two orders of magnitude.  (The
   exact amount of savings depends on the relative number of home users
   compared with the number of larger sites.)

   The above-mentioned goals of RFC 3177 can easily be met by giving
   home users a default assignment of less than /48, such as a /56.

Royce



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