which program for bandwidth monitoring?

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http://www.linuxforums.org – Hello, Im looking for a program to monitor the ammount of bandwidth usage per network. Ex: I have lots of networks connected to one server, and i would like to know for example how much is the average bandwitdh usage for network and for one hour, for example. Which program you guys suggest me to use for that? I dont need a graphic interface for the program, console is fine. thanks. (HowTos)