[bonyt]

Does each container network of the 256 really need its own /64? Is there some constraint that doesn't let them work on a /72?

[yrro]

In practice this can be made to work but a networking expert can probably explain better than me why splitting a prefix into chunks smaller than a /64, and assigning them to virtual networks within a host is a bad idea.

In Hetzner's specific case: they won't give me one or more additional /72s: only a /56 if I pay for it. Per server.

[kazen44]

splitting things out in a smaller prefix then a /64 breaks a couple of things. SLAAC will not work, and slaac is actually a really neat usecase for containers. Not having the overhead of DHCP for container addressing is neat. Also, smaller blocks then /64 makes things like prefix delegation (usually) also break from a provider.

[matt-p]

A container should absolutely not even need a /72. The traditional reason for /64 is for slaac but you most certainly don't need that for one container (if at all honestly).

[yrro]

Indeed, a host should be able to request a /64 via DHCPv6-PD and split that between millions of container networks. But you can't do that on Hetzner (or anywhere else).