linux – persistently disable ping/ICMP response on Ubuntu 20.04

It was possible to add net.ipv4.icmp_echo_ignore_all = 1 to /etc/sysctl.conf and reload with sysctl -p.

This does work for me on Ubuntu 20.04.

But after a reboot, the machine responds to ICMP requests again.

Why is that, and is there a fix?

Thanks in advance.