How to route IPv6 to the external interface?

I have purchased a VPS from IONOS. While they provide an IPv6 range 2a00:xxxx:xxxx:67::/64, they don't route it to the VPS itself, which is quite odd.

I wonder how I can achieve that. I have only 254 clients, so I'm happy to do it manually. This is what I already see in the route table:

ip -6 route

::1 dev lo proto kernel metric 256 pref medium
2a00:xxxx:xxxx:67:ffff::1 dev wg0 metric 1024 pref medium
2a00:xxxx:xxxx:67:ffff::2 dev wg0 metric 1024 pref medium
... all way to 254
2a00:xxxx:xxxx:67:ffff::254 dev wg0 metric 1024 pref medium
2a00:xxxx:xxxx:67::/64 dev ens192 proto kernel metric 256 pref medium
fd8e:xxxx:xxxx::/112 dev wg0 proto kernel metric 256 pref medium
fe80::/64 dev ens192 proto kernel metric 256 pref medium
default via fe80::1 dev ens192 metric 1024 onlink pref medium

So do I need to assign the client IPs separately to the ens192 to make this work? I have made a small bash script for this:

#!/bin/sh
NUMBER_CLIENTS=254
for ((DOT_IP=1; DOT_IP<=NUMBER_CLIENTS; DOT_IP++))
do
        sudo ip -6 addr add 2a00:xxxx:xxxx:67:ffff::${DOT_IP}/64 dev ens192
done

The script works, but my Wireguard VPN clients still don't get a functioning IPv6. After successfully connecting with Wireguard, they have only an IPv4 assigned and not an IPv6.

What else could I do please?

Based on their guide, they seem to be suggesting to use accept_ra 0 in the static IP allocation. But I didn't set it:

auto lo ens192
iface lo inet loopback

allow-hotplug ens192
iface ens192 inet dhcp

iface ens192 inet6 static
  address 2a00:xxxx:xxxx:67::1
  netmask 64
  gateway fe80::1

Other than that I have forwarding enabled in /etc/sysctl.d/99-sysctl.conf:

net.ipv4.ip_forward = 1
net.ipv6.conf.all.forwarding = 1

Many Thanks

I recently had a similar issue. On IONOS VPS using their default config, IPv6 unfortunately stops working when enabling net.ipv6.conf.all.forwarding = 1. This is specific to the IONOS setup, because they use "router advertisement" to determine the true IPv6 address, probably to avoid having to create a specific interfaces file for each VPS when deploying the image. Their default IPv6 config looks as follows:

iface ens192 inet6 manual
      pre-up sleep 5
      up dhclient -6 -nw -v ens192
      down dhclient -6 -r -v ens192

IP6 forwarding however disables router advertisement by default, so IPv6 stops working in that case.

A working solution to that issue is the following IPv6 config in /etc/network/interfaces (replace the address with your VPS' specific IPv6 address, a reboot may be advisable):

iface ens192 inet6 static
        accept_ra 2
        address 2a00:xxxx:xxxx:67::1/128
        up ip -6 r a default dev ens192

The accept_ra 2 forces router advertisement, but this parameter is ignored for the 'manual' method, therefore the 'static' method.