Private use of non-RFC1918 IP space (IPv6-MW)

Scott Howard scott at
Wed Feb 4 23:56:44 UTC 2009

On Mon, Feb 2, 2009 at 9:30 PM, Anthony Roberts <nanog at
> wrote:

> It has been my experience that when you give someone a huge address space
> to play with (eg 10/8), they start doing things like using bits in the
> address as flags for things. Suddenly you find yourself using a prefix
> that should enough for a decent sized country in a half-rack.

Which is, of course, a core design philosophy for IPv6. Stateless autoconfig
relies on the fact that each network will be allocated 2^64 address.

On Mon, Feb 2, 2009 at 9:35 PM, Patrick W. Gilmore <patrick at>wrote:

> Except the RIRs won't give you another /48 when you have only used one
> trillion IP addresses.

Of course they will!  A /48 is only the equivalent of 65536 "networks" (each
network being a /64).  Presuming that ISPs allocate /64 networks to each
connected subscriber, then a /48 is only 65k subscribers, or say around a
maximum of 200k IP addresses in use at any one time (presuming no NAT and an
average of 3-4 IP-based devices per subscriber)

IPv4-style utilization ratios do make some sense under IPv6, but not at the
address level - only at the network level.


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