[off-topic] Re: [address-policy-wg] 2008-01 Moved to Review Phase (Assigning IPv6 PI to Every Inetnum Holder)

> > a /56 is a tad over 1000 networks, each the size of the entire IPv4 
> > space.
> 
> this is a little fallacy we keep playing on ourselves.  it is 
> only usefully true if you think you will be deploying 
> absolutely jigongous layer two flat networks of O(2^64) size. 
>  and we all know that's not possible.
> 
> or are you suggesting that we all throw the /64 magic lan 
> boundary back in the ietf's face at this late date?  while 
> this would not break my little black heart, i don't think 
> it's very likely to succeed.

If we accept that an IPv6 subnet prefix can be no longer than /64
then there are 8 bits between /56 and /64, that can be used to
design a subnetting hierarchy. This is HALF the number of bits
that is available with a standard site allocation of /48.

Since these prefix sizes (/48 and /64) were agreed on in order
to give subnets more bits than they could possibly need, and
sites more bits than they could possibly need, I think it is
reasonable to question a plan which gives organizations, possibly
with multiple sites, only a single /56. This goes against the
fundamental architecture of IPv6 which tries to give every
network (ISP, site, subnet) enough bits to allow them to
expand within their assigned prefix without needing to rearchitect
whole sections of their network.

Of course, there is a much better argument against this proposed 
allocation and that is that it is pointless to give stuff to
organizations who have no need of it, when it is simple and cheap
for them to get the same stuff (or better) when they do have the need.

But I still think that it needs to be pointed out that the standard
prefix lengths of /64 for a subnet, /48 for a site, and /32 for an
ISP, provide real benefits in network architecture and design. We should
never make changes to this architecture without considerable thought
and understanding of the reasons why these prefix lengths were chosen.

IPv6 is not the same as IPv4.

--Michael Dillon