Debian Bookworm -> Trixie upgrade - systcl troubles

I’ve been running Debian on a PCengine apu2 for a very long time now. I’ve upgraded it from buster to bullseye to bookworm and now.. to trixie.

The upgrade process went well, but i had one issue after rebooting the system - masquerading (or ip forwarding) didn’t work anymore. I invested time in setting up nft for my firewall, so I initially expected some issues there. The /etc/nftables.conf file was applied correctly at startup though.

I turned out that /etc/sysctl.conf was no longer being used. It was renamed to /etc/sysctl.conf-dpkg-bak and wasn’t executed at startup. Instead, I had to create a whatever.conf file in /etc/sysctl.d/. The content of that file is the same as before. The filename doesn’t matter, as long as it ends with .conf.