Blocking ICMP outgoing requests only in eth1

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http://serverfault.com – I am creating a NAT with iptables: Computer A: eth0 (dhcp) + eth1 (static ip - gateway) Computer B: eth1 (static ip, using Computer A as gateway) I know how to block ICMP outgoing requests (-A OUTPUT -p icmp --icmp-type echo-request -j DROP), but that would block ICMP requests from Computer A, but not from Computer B (in fact, only for Computer A - Computer B can keep doing those). I tried with the same command, but adding -o eth1, but that does not block at all. Any idea? (HowTos)