iftop: Real-time network performance data under Linux

[Wrigleyvillain]

iftop is a Linux command-line program designed to give you live statistics about what network connections use the most bandwidth in a nice graphical form. As you may realize from the name, iftop borrows a lot of ideas from the always-useful load troubleshooting tool top. Like top, iftop updates automatically every few seconds, and like top, by default, it sorts the output you see by what's using the most resources. Where top is concerned with processes and how much CPU and RAM they use, iftop is concerned with network connections and how much upload and download bandwidth they use.

Linux Journal

[SIGSEGV]

awesome and simple network traffic monitoring application, also it's very useful especially for router server or dedicated server environment.