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

TJ trejrco at
Thu Feb 5 01:45:22 UTC 2009

>> 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.
>First, it was (mostly) a joke.
>Second, where did you get 4 users per /64?  Are you planning to hand each
>cable modem a /64?

No, we should hand each home a /56 (or perhaps a /48, for the purists out
there) - allowing for multiple segments (aka subnet, aka links, etc.).  Note
- the actual number of hosts is irrelevant; the 64 bits on the host side of
the address are not meant to encourage 18BB hosts/segment.

Oh, and utilization should be based on /56s anyway.


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