Shorewall
From Indie IT Wiki
Shoreline Firewall (Shorewall) Tips
To list the connections from an IP address.
conntrack -L -s 192.168.0.103
To drop all the connections from an IP address.
conntrack -D -s 192.168.1.102
It can take up to 1 minute to drop all of them, so be patient. You can then restart shorewall and be certain any NEW connections (not ESTABLISHED ones) will be accounted for.
Block An IP Address
shorewall drop {IP-ADDRESS}
Allow An IP Address
shorewall allow {IP-ADDRESS}