minimum IPv6 announcement size

Joe Abley jabley at
Fri Sep 27 14:54:48 UTC 2013

On 2013-09-27, at 10:40, Brandon Ross <bross at> wrote:

> On Fri, 27 Sep 2013, Ryan McIntosh wrote:
>> It's a waste, even if we're "planning for the future", no one house
>> needs a /64 sitting on their lan.. or at least none I can sensibly
>> think of o_O.
> Okay, I'm just curious, what size do you (and other's of similar opinion) think the IPv6 space _should_ have been in order to allow us to not have to jump through conservation hoops ever again?  128 bits isn't enough, clearly, 256?  1k?  10k?

Given the design decision to use the bottom 64 bits to identify an individual host on a broadcast domain, the increase in address size isn't really 32 bits to 128 bits -- if your average v4 subnet size for a vlan is a /27, say, then it's more like an increase of 27 bits to 64 bits from the point of view of global assignment.

Alternatively, considering that it's normal to give a service provider at least a /32, whereas the equivalent assignment in v4 might have been something like a /19 (handwave, handwave), it's more like an increase of 13 bits to 32 bits.

Alternatively, considering that it's considered reasonable in some quarters to give an end-user a /48 so that they can break out different subnets inside their network whereas with IPv4 you'd give a customer a single address and expect them to use NAT, then it's more like an increase of 31 bits to 48 bits.

That's still a lower bound of 2^17 times as many available addresses, and having enough addresses to satisfy a network 131,072 times as big as the current v4 Internet does not seem like a horrible thing. But the oft-repeated mantra that "there are enough addresses to individually number every grain of sand on the world's beaches" doesn't describe reality very well.

The IPv6 addressing plan didn't wind up meeting our requirements very well. Film at 11.


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