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i want to know what is the difference between these two commands

iptables -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT


iptables -A INPUT -p tcp --dport 80 -j ACCEPT
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Nothing, since the tcp match is implicit when filtering the tcp protocol.

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SO IT MEANS -m option is only important for STATE matches , otherwise no need to use for tcp , udp , icmp –  John Aug 26 '10 at 6:23
If either no options imply a match or if an option implies multiple matches then you need to specify a match. Otherwise, iptables will figure out what you mean in the command line. –  Ignacio Vazquez-Abrams Aug 26 '10 at 6:43

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