Wow, so the issue is that our ISP (also a Linode VPS customer here) assigns us a /64 address, our virtual neighbors suck up “our” registrations and then we can’t register or request a certificate?
On first blush that seems like bad design from the get-go; however, thinking deeper into it one of the perks of IPv6 is being able to just hand over big chunks of addresses to anyone who wants them, which means that the average Joe Blow IPv6 user could trivially bypass any IP-based rate-limiting, possibly without even knowing he’s doing it, if you took the “naive” IPv4-based approached of sticking to just a single address for rate-limiting purposes.
Is there a way to restrict the client to use IPv4, or to tell it to use a particular (virtual) network adapter when sending the request?