You can learn an amazing amount of information about your network connections with these three glorious Linux networking commands. iftop tracks network connections by process number, Nethogs quickly reveals what is hogging your bandwidth, and vnstat runs as a nice lightweight daemon to record your usage over time. iftop The excellent iftop listens to the network interface that you specify, and displays connections in a top-style interface.
Source: 3 Simple, Excellent Linux Network Monitors