A list of useful networking monitoring tools. This is not a Top 10 or Top 5 or Top whatever, the usefulness of these applications depends on your environment and what exactly you want to monitor for.
ntop is a network traffic probe that shows the network usage, similar to what the popular top Unix command does. ntop is based on libpcap and it has been written in a portable way in order to virtually run on every Unix platform and on Win32 as well. It’s great to use, comes with a list of plugins and has a nice web-interface. It’s an easy an inexpensive way to catch misconfigured or compromised hosts on your network.
tcpdump is probably the best known monitoring tool, it dumps all the network traffic and comes with extended filtering capabilities.
atop is an advanced interactive monitor for Linux-systems to view the load on system-level and process-level but it can also display the network traffic. Start it with atop -N > file.
bmon is a bandwidth monitor for network connections. With it you can watch a certain network card or a many of them. Bmon presents the results in ascii or ncurses.
6. nfsen / nfdump
nfsen is an open source netflow monitor. Results are presented via a webinterface and it comes with tcpdump-like filters. Invaluable tool for network analysis.