Telekom enforces a PPPoE reconnect every 180 days, O2 however enforces a PPPoE reconnect every 24 hours (after the last connect). In both cases both IPv4 and IPv6 addresses/prefixes will change. The way around that is to use some sort of dynamic DNS service. And if you want to offer IPv6 services from your home network you need to configure your firewall accordingly. OpenWrt allows to mask out the non-inrerface-identifier portion of IPv6 addresses, so firewall rules can survive a prefix change.

It changes every 24 hours… I base this on my recorded data (I run a few traceroutes every night and store the IPv6 prefix as part of my book keeping). If you need persistent addresses, maybe consider getting a business tarif, where IIRC persistent addresses are an option. Or consider dynamic DNS as a work-around.

@pufferueberlauf0 Thanks a lot for the detailed answer!

Yes, I’m already using a dynamic DNS service, there are no issues with that. I’m also using oauth2 authentication for connections coming from the internet. For LAN connections I don’t want to have any authentication. This works for ipv4, but with ipv6 I can’t reliably identify whether it’s from my LAN or it’s another subnet. I have a couple of ideas (using a kind of VPN or dynamically update oauth2 rules), but they’ll requre some effort to implement.

Intersting! Alas, I have zero experience with oauth2, so I have nothing to contribute here. Good luck!