AWS and IPv6

Sun Nov 28 22:10:40 UTC 2021

On Sun, Nov 28, 2021 at 1:18 PM Karl Auer <kauer at biplane.com.au> wrote:
> On Sun, 2021-11-28 at 12:53 -0800, Michael Thomas wrote:
> > I was reading their howto yesterday and it seems they are only
> > allocating a /64? Why?
>
> That's a /64 *per subnet*...
>
> But the size of a VPC's IPv6 CIDR block does seem to be fixed at /56.
> Would have been nice to see /48 instead.

Hi Karl,

To what purpose? You can't alter the VPC routing of any of the IP
addresses (v4 or v6) assigned to an AWS VPC. If you try, for example,
to assign a /64 to an instance you get a funky error: "Route
destination doesn't match any subnet CIDR blocks." You can only assign
the block's IP addresses to subnets or not and then assign addresses
from the subnet to the instances. You can't have more than 256 subnets
in a VPC so why would you need more than a /56 of IPv6 addresses?

Regards,
Bill Herrin

-- 
William Herrin
bill at herrin.us
https://bill.herrin.us/