iftop

Iftop is a free software command-line system monitor tool developed by Paul Warren. It produces a real-time stream of incoming and outgoing network communications from the operating system iftop is running within.[2] By default, the connections are ordered by bandwidth usage, with only the largest ("top") bandwidth consumers shown. It is analogous to top, but instead of system-wide resource monitoring, it focuses on displaying just network usage. Iftop is typically used for monitoring bandwidth consumption, and while investigating unknown consumers of available network bandwidth.