I am trying to set up this rule :

 iptables -A INPUT -i eth1 -p tcp -s ! --dport ssh --syn -m state --state NEW -j ACCEPT

but it doesnt work. When i change place of !

 iptables -A INPUT -i eth1 -p tcp ! -s --dport ssh --syn -m state --state NEW -j ACCEPT

its ok but i am not sure is it working correctly. In every tut on net "!" is between -s and ip not in front of it.

  • Could you clarify "it doesn't work"? And you are escaping that !, aren't you?
    – MadHatter
    Dec 12, 2013 at 21:48
  • I must say, iptables is extremely powerful, but it's command line interface crap. FreeBSD's ipf is significantly easier to understand in my opinion although I haven't used it in a long time.
    – hookenz
    Dec 12, 2013 at 22:00

1 Answer 1


Your second example is correct.

The first example is an old and deprecated way of writing such rules; current versions of iptables will print a warning, or refuse the rule entirely, if you use it.

Old tutorials on the Internet, of course, have old information.


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