iftop

Display bandwidth usage on an interface by host

iftop listens to network traffic on a named interface, or on the first interface it can find which looks like an external interface if none is specified, and displays a table of current bandwidth usage by pairs of hosts. iftop must be run with sufficient permissions to monitor all network traffic on the interface; see pcap(3) for more information, but on most systems this means that it must be run as root.