iptables don't drop icmp packets

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http://serverfault.com – I wanna block ping from outside the company to my server, so I have the following iptables rules: -A INPUT -p icmp --icmp-type 8 -s ! -j DROP -A OUTPUT -p icmp --icmp-type 0 -d ! -j DROP However, the above rules aren't working as expected, I can still ping the server from both inside and outside the company. What's wrong with that?! (HowTos)