Current Consensus on IPv6 Customer Allocation Size

Doug Barton dougb at
Thu Aug 2 00:34:31 CEST 2012

On 8/1/2012 2:12 PM, Mark Blackman wrote:
> On 1 Aug 2012, at 22:03, Tim Densmore <tdensmore at> wrote:
>> - It's "easy" to forsee that someday in the future people will need more than 256 subnets in the home, and since nibble boundaries are considered a must, then /48 is the only option.
> More than 256 subnets in the home? Who would want to manage all of that?

As Chris pointed out there is a theoretical (not unlikely, just not here
yet) future where we will have massive, smart, cascading home networks.
So, since v6 addresses are not scarce, why not allow for this to happen
in the initial phases of planning?

However, as you correctly point out Mark, hand a user a /48 and they're

So, the plan I have been advocating for years now is to do what the RIRs
are doing. Start your addressing plan by *reserving* the largest block
you think may be reasonable for each customer, but today you only assign
something more manageable. That way you can always go back and let a
power user expand into their reservation without disrupting anything.
And if down the road you end up with reservations that you're confident
are excessive, you can divide them and start the reservation/assignment
process over.

So in Tim's case I'd reserve a /48, and assign the first /56 from it.
Personally I think a /60 is more than enough for a home user nowadays,
but IIRC ARIN's guidance on utilization mentions a /56. (You're on your
own to research/confirm that though.) :)

And Tim, one other factor you alluded to that I think it's worth making
explicit. You want to keep the assignments on the nibble boundaries
because it makes DNS management easier.



	If you're never wrong, you're not trying hard enough

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