Joined: 28 Oct 2002 Posts: 16777215 Location: Chicago, IL US
Posted: Tue Sep 21, 2010 3:08 pm Post subject:
Actually libpcap will see the packet before it is handled by netfilter. So if your iptables denies ICMP and you try to ping the host, tcpdump will show the ICMP echo requests but the firewall will dump the traffic.
Now, I can't remember offhand, but I think the prerouting chain might be different. So if you do some NATing, prerouting might muck with the packet before libpcap sees it. Not positive so test it out on your own if that's important for your results.
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