"Visually sniffing with Wireshark
"If you don't particularly enjoy the command-line or are a Linux
newbie, you might want to stick with using a GUI-based sniffer.
Additionally, using a visual application can provide a faster and
more in-depth inspection of your network traffic. We're going to
look at Wireshark, a popular cross-platform network analyzer,
formally named Ethereal.
"Once you open Wireshark, click Capture > Interfaces and
click the Start button for the desired interface to start
capturing. Packets should start appearing, such as seen in Figure
1. To inspect a packet, select it from the list. Then you can
browse through the packet details and see the actual contents in
HEX and ASCII.
"To prevent Wireshark from resolving hostnames or port names,
click Capture > Interfaces and hit the Options button for the
desired interface. Then in the bottom-right corner of the Options
window, change the Name Resolution settings as you wish."