A port is simply a number that is embedded in a UDP packet header. There is a destination and a source port number in every UDP packet. The destination port is used by a computer to direct incoming packets to the intended program. For example, a program that pops-up Caller ID information could be setup to only allow packets with the port number 3520. It would ignore UDP packets with any other port number. The default factory setting is 3520 for both the destination and source port number. The destination port number can be changed, if needed, using the setup program supplied. In the above Wireshark illustration, the ports are the first four Hex numbers in green; 0D C0 0D C0. The first 0D C0 is the source port binary number; the second 0D C0 is the destination port – both equal 3520 decimal.