The following iptables rule is used to redirect all internet traffic coming in from eth1 to port 3000 at localhost (interface lo with ip 127.0.0.1):
iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 80 -j DNAT --to-destination 127.0.0.1:3000
Then tcpdump is set up to record all traffic at the lo interface:
tcpdump -i lo -w output.dump
However, after I sent some internet traffic (port 80) through eth1, this traffic is not recorded by tcpdump.
I am not sure why this is so. Can someone please shed some light? Thanks.