"One of my favorite utilities in the ports collection is the
network analyzer, Ethereal. I've used NT's Network Monitor and
Novell's Lanalyzer, but I've found that neither matches the
functionality of Ethereal."
"If you've never used a network analyzer before, you may wonder
why you'd want to use such a utility. If a network administrator is
experiencing slow network performance, a network analyzer can help
him pinpoint which NICs, cable segments, and protocols are
generating the most traffic. The results can be used to determine
if he needs to upgrade his cabling, change a faulty NIC, install a
bridge, reorder his network bindings, consider using less chatty
"A security engineer can use the results to determine if his
firewall system is responding to requests according to his security
"And finally, the results of a network analyzer provide the best
learning environment to gain a practical understanding of the OSI
model and how protocols actually interact with each other."