I have a linux machine (turnkey core 14.2) with two network cards.
eth0 is a public ip, WAN (let's call it 123.123.123.123).
eth1 is my network, LAN.
I would like to block SSH from the WAN with iptables.
I use the command
sudo iptables -A INPUT -p tcp -s 123.123.123.123 --dport 22 -j DROP
If I then write
sudo iptables -L
I get the answer
Chain INPUT (policy ACCEPT)
target prot opt source destination
DROP tcp -- 123.123.123.123 anywhere tcp dpt:ssh
Problem is that I'm not blocked if I use PuTTY to connect to 123.123.123.123.
Any idea what I'm doing wrong?
You are matching traffic by source address (-s option), instead of destination address (-d option), which is why your rule doesn't drop any traffic from other hosts.
You can also match by input interface (instead of address) with -i option. For example to drop all incoming traffic to port 22 for eth0:
iptables -A INPUT -i eth0 -p tcp --dport 22 -j DROP
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