/etc/sysctl.conf is not used anymore. Use /etc/sysctl.d directory.
It was discussed here a few days ago, see man sysctl.conf(5) Am 28.01.26 um 19:52 schrieb Joe:
On Wed, 28 Jan 2026 16:36:28 +0100 Nicolas Kovacs <[email protected]> wrote: First check what systemd knows about IP forwarding. Either # sysctl net.ipv4.ip_forward # cat /proc/sys/net/ipv4/ip_forward will return 0 for disabled, 1 for enabled. If you get a 0 return, try # echo 1 > /proc/sys/net/ipv4/ip_forward and see if forwarding is now working. If so there is a line in /etc/sysctl.conf: net.ipv4.ip_forward = n which may be either zero or commented out, set it to 1. There is also a .d directory alternative (better) where you may create this line in a numbered file, and maybe need to create the directory first. It's easiest to check that it works first as a line in sysctl.conf. Debian and I think other distributions disable forwarding by default i.e. it must be user-enabled. I don't believe any firewall enables it automatically. There are many places where it may be set during boot, in a script, so best check first whether it is already enabled and the problem is somewhere else.
