Just another handy snippet:
It will date the output, and also put it in a handy pcap for Wireshark.
tcpdump -i eth1 -s0 -v -w /tmp/capture_`date +%d_%m_%Y__%H_%I_%S`.pcap
*Note: Should work on all Linux distros (make sure to have the right network interface selected, Ex: eth1); it might have to be slightly modified for Mac. Windows can go DIAF.