Fail2ban comes preinstalled with FreePBX bundle. This is how to remove a banned IP address from the Fail2ban DROP list manually:
fail2ban-client status asterisk
iptables -L --line-numbers
***@raspbx:~# iptables -L --line-numbers
Chain INPUT (policy ACCEPT)
num target prot opt source destination
1 fail2ban-asterisk tcp -- anywhere anywhere tcp dpt:sip
2 fail2ban-asterisk udp -- anywhere anywhere udp dpt:sip
3 fail2ban-asterisk tcp -- anywhere anywhere tcp dpt:sip-tls
4 fail2ban-ssh tcp -- anywhere anywhere multiport dports ssh
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
Chain fail2ban-asterisk (3 references)
num target prot opt source destination
1 DROP all -- 192.168.*.** anywhere
2 RETURN all -- anywhere anywhere
Chain fail2ban-ssh (1 references)
num target prot opt source destination
1 RETURN all -- anywhere anywhere
***@raspbx:~# iptables -D fail2ban-asterisk 1
***@raspbx:~# fail2ban-client stop
^[[A^[[BShutdown successful
***@raspbx:~# fail2ban-client start
WARNING 'ignoreregex' not defined in 'Definition'. Using default one: ''
2015-02-22 11:25:55,768 fail2ban.server [7466]: INFO Starting Fail2ban v*.*.**
2015-02-22 11:25:55,770 fail2ban.server [7466]: INFO Starting in daemon mode
***@raspbx:~# fail2ban-client status asterisk
Status for the jail: asterisk
|- filter
| |- File list: /var/log/asterisk/security_log
| |- Currently failed: 0
| `- Total failed: 0
`- action
|- Currently banned: 0
| `- IP list:
`- Total banned: 0