IPv6 Default Allocation - What size allocation are you giving out

Thu Oct 9 05:06:23 UTC 2014

Mark,

>> >Only short sighted ISP's hand out /56's to residential customers.

>>
>> I am curious as to why you say it is short sighted? what is the technical or
>> otherwise any other reasoning for such statement ?
>
>256 is *not* a big number of subnets.  By restricting the number
>of subnets residences get you restrict what developers will design
>for.  Subnets don't need to be scares resource.  ISP's that default to
>/56 are making them a scares resource.

The excerpt Royce quoted from RFC6177 (requoted below) seems to back away 
from /48s by default to all resi users and land in a somewhat vague "more 
than a /64 please, but we're not specifically recommending /48s across the 
board for residential" before specifically mentioning /56 assignments.

The general push in the community is towards /48 across the board.  Any 
comments on why the RFC backs away from that?  Is this just throwing a bone 
to the masses complaining about "waste"?

btw: hat tip to Peter Rocca for a kind of scale we're talking about for 
allocatable space.

--
Hugo

>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.
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