To install fail2ban on Ubuntu 24.04
apt-get install fail2ban
Check if there are any new sessions
zgrep "New session" /var/log/auth.log*
Check what jails are enabled
fail2ban-client status
Now check the ssh jail that is enabled
fail2ban-client status sshd
To check the currently banned IPs
grep 'Ban' /var/log/fail2ban.log*
These are the fail2ban defaults for your Ubuntu server
/etc/fail2ban/jail.d/defaults-debian.conf -- the defaults
Get what are the default actions for the ssh jail
fail2ban-client get sshd actions
By default the command above gives nftables.
To get the blocked IPs
nft list ruleset
Reference
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