NAST (Network Analyzer Sniffer Tool) is an ncurses-based tool that has, admittedly, not been under development for quite some time. Even so, the tool is quite useful and does a great job of capturing network traffic. I put this tool on the list because it's invaluable if the only machine you have access to is a UNIX GUI-less server. But even if you have a GUI, this tool is quite handy.
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