You can find information about your network connections using netstat.
# t = Show sockets using the TCP protocol.
# u = Show sockets using the UDP protocol.
# l = Show only listening sockets.
# p = Show the PID and name of the program to which each socket belongs.
# n = Show numerical addresses instead of trying to determine symbolic host, port or user names.
$ sudo netstat -tulpn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:17500 0.0.0.0:* LISTEN 2228/dropbox
tcp 0 0 127.0.0.1:17600 0.0.0.0:* LISTEN 2228/dropbox