tcptrack is a sniffer which displays information about TCP connections it
sees on a network interface. It passively watches for connections on the
network interface, keeps track of their state and displays a list of
connections in a manner similar to the unix 'top' command. It displays
source and destination addresses and ports, connection state, idle time, and
bandwidth usage.

WWW: http://www.rhythm.cx/~steve/devel/tcptrack/