I made a clean install of Debian bullseye (netinstall). fail2ban fail becouse default instalation use iptables, not nftables I guess the package uses iptables for compatibility, but in clean installations it fails because it does not use nftables. I don't know if this configuration can be added by default on clean installs in the file /etc/fail2ban/jail.d/defaults-debian.conf the lines: [DEFAULT] banaction = nftables-multiport banaction_allports = nftables-allports