Debian 12 DHCPv6 issues

[llek]

I do not know if this is the correct forum for this, please let me know if it's not.

Hello, I have a slightly complicated setup, basically my ISP only gives me an IPv4. I then have a VPN client setup to a VPS that gives me "fddd:2c4:2c4:2c4::1/64" this all works fine.
I have the LAN static IPv6 set to 2001:db8::1/64 and the DHCP range to "2001:db8::2 - 2001:db8::ffff:ffff:ffff:ffff". Now Windows devices work fine, they seem to grab the IPv6 from the DHCP server, as I can see it in the DHCPv6 server leases - and I can access local devices like cisco access points, other windows devices and also WAN.
The problem is with Linux devices, now I've had Linux devices setup with "iface enp4s0 inet6 auto" - this has worked fine, but I was not able to see the devices in DHCPv6 leases as I think it was using stateless config.
When I set it to "iface enp4s0 inet6 dhcp" I only get one /128 IPv6 and I am not able to ping either anything on the local network or anything on WAN side.

I am completely out of ideas now, yes, I could use stateless, but I would like to see the devices in DHCPv6 leases if it's possible.
Sorry for the very confusing explanation, I've been trying to get this to work for about 7 hours now.

Thank you for any help!

[MenschAergereDichNicht]

Hi!

I don't think that i completely understood you problem. But i also struggle with IPV6 connectivity in Debian 12.

In my case i try to get a working SLAAC setup as this is what my mobiles seem to like. On the other hand my linux notebook with Debian 12 at first had only a link local IPv6 address. I tried to tweak it with several sysctl settings until i realised that it was using NetworkManager. Because that is new territory for me i disabled the IPv6 handling of NetworkManagerit for that connection (nmcli c m <WLAN Connection> ipv6.method ignore).

Now i have at least several IPv6 addresses. I still have connection problems which may be related to a missing default gateway... .

Long story short. I think the combination of NetworkManager and Ipv6 is a little bit special and may need some trial and error to get right.