apt-get install iftop

ifconfig

iftop -i eth0

iftop: display bandwidth usage on an interface by host
Synopsis: iftop -h | -npbBP -i interface -f filter code -N net/mask
  -h                  display this message
  -n                  don't do hostname lookups
  -N                  don't convert port numbers to services
  -p                  run in promiscuous mode (show traffic between other
                      hosts on the same network segment)
  -b                  don't display a bar graph of traffic
  -B                  Display bandwidth in bytes
  -i interface        listen on named interface
  -f filter code      use filter code to select packets to count
                      (default: none, but only IP packets are counted)
  -F net/mask         show traffic flows in/out of network
  -P                  show ports as well as hosts
  -m limit            sets the upper limit for the bandwidth scale
  -c config file      specifies an alternative configuration file
iftop, copyright (c) 2002 Paul Warren <pdw@ex-parrot.com> and contributors