List all internet connections
Using netstat
netstat by itself monitors all major protocols including TCP and UDP on every port.
If you want to display TCP and UDP connections:
netstat -t -u
If you want to display that continously:
netstat -t -u -c
Similar to top:
nethogs - shows a list of the top processes that use bandwidth
jnettop - shows list of top connections
iftop - shows list of top connections with bandwidth bars
GUI Interface (just in case):
Ntop
Netactview