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I have a firewall with these simple rules:

iptables -A INPUT -p tcp -s --dport 6000 -j ACCEPT
iptables -A INPUT -p tcp -s --dport 6000 -j ACCEPT
iptables -A INPUT -p tcp --dport 6000 -j REJECT

Now, suppose I am using TCPDUMP like this:

tcpdump port 6000

And I have host trying to connect to port 6000.

Will/should tcpdump output some packets coming from

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up vote 8 down vote accepted

tcpdump uses libpcap and libpcap processes packets before they get processed by the firewall, so the answer is "yes".

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