after seeing the announcement about vultr in another thread, I took a closer look at ipv6 support and it looks like DO and scaleway do not provide a proper /64 for IPv6 -- or even a /112, which means you can't use openvpn.
unless it has changed or varies by datacenter, DO issues a /124 by default -- I've confirmed this on my own droplets just now. issuing a /64 is "proper" because it is RFC[1].
Super late reply, but I just wanted to correct myself. I don't have a /64 on DO. I was confusing my DO config with something else. I'm sorry about that. You are correct.
