[ppml] [address-policy-wg] Re: IPv6 addresses really are scarce after all

michael.dillon at bt.com michael.dillon at bt.com
Fri Aug 31 11:31:50 EDT 2007

> Will all due respect, even if you assume a "home" with ten 
> occupants, a few hundred subnets based on functions, and 
> enough sensor-type devices to estimate several thousand of 
> them per occupant and a few thousand more per room, 2**64 is still a
> _lot_ of addresses.  

This is hyperbole. All IPv6 subnets have the same minimum number of
addresses (2**64) regardless of where they are used.

>  But I don't think hyperbole 
> helps the discussion.

I agree. In any case, it doesn't make sense to discuss IPv6 in terms of
hostcounts. It makes more sense to discuss numbers of subnets or numbers
of aggregation levels.

If a private home with two occupants and one PC, builds out an in-law
suite for one mother-in-law with one PC, then it still makes sense to
have at least two subnets in that private home, i.e. at least one level
of aggregation. Hostcount is irrelevant. Note that if both mother-in-law
and homeowner install 4 or five home media devices, the subnetted
architecture will work better than a /64 per home scenario.

Now that we have shown subnetting is useful in a private home, it is
clear that a /64 per home is not enough.

It still leaves open the question of whether a /48 is too much, i.e. too
many subnets and/or too many levels of aggregation. If a /48 is not too
much, then the IETF should issue guidance that states that. If some
prefix length between /48 and /64 is OK under certain circumstances then
the IETF should issue guidance which states that. I still have not seen
any clear indication that there is a negative technical impact of
assigning a /56 per home. To date, the only clear technical issue I have
seen mentioned for subnet prefixes longer than /48 is that if they are
not on a 4-bit hex nibble boundary, it makes IPv6 PTR delegation more

--Michael Dillon

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