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I want to stop internet on my system using iptables so what should I do?

iptables -A INPUT -p tcp --sport 80 -j DROP

or

iptables -A INPUT -p tcp --dport 80 -j DROP ?

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You went from "I want to allow only some specific services like I should be able to access the internet" to "I want to stop internet on my system"? –  Michael Mrozek Sep 11 '11 at 5:58
    
Trying different modes of iptables. –  Chankey Pathak Sep 11 '11 at 6:11
    
@Chankey I'd advise reading the stateful firewall article I linked in my other answer, it will probably explain everything you need to know how to do. It's very easy too.. just ignore emerge and kernel config parts. –  xenoterracide Sep 11 '11 at 6:34
    
Okay, thank you xenoterracide :) –  Chankey Pathak Sep 11 '11 at 6:36
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1 Answer

up vote 4 down vote accepted

Reality is you're asking 2 different questions.

  • --sport is short for --source-port

  • --dport is short for --destination-port

also the internet is not simply the HTTP protocol which is what typically runs on port 80. I Suspect you're asking how to block HTTP requests. to do this you need to block 80 on the outbound chain.

iptables -A OUTPUT -p tcp --dport 80 -j DROP

will block all outbound HTTP requests, going to port 80, so this won't block SSL, 8080 (alt http) or any other weird ports, to do those kinds of things you need L7 filtering with a much deeper packet inspection.

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