TCPDump is an extremely handy tool for verifying if packets are getting to the linux box or not. Here are the commands I use most often:
To specify which interface to listen on:
tcpdump -i eth1
To specify which IP address to listen for (will listen to both source and destination):
tcpdump host 10.64.45.53
To specify a port that is either source or destination:
tcpdump port 8080
To specify a source port use:
tcpdump src port 8443
To specify a destination port use:
tcpdump dst port 514
And of course you can add all of that together in one line using the “and” keyword:
tcpdump -i eth1 host 10.64.45.53 and port 8080
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