This particular line is for viewing 1300 bytes (or less) of each packet sent out on a multicast address 224.0.6.127 (Oh Mighty ISIS). -x and -X provide hex and ascii translation.
tcpdump -x -X -s 1300 -i eth0 -- host 224.0.6.127
Adam Young's Web Log
The Notebook of a Programmer Climber Musician Ex-Soldier Woodworker and a few other things
