Port & Socket numbers

A port number is a number that identifies different services that run on a PC or device using TCP or UDP (layer 4), while a socket number is an IP address with the port number included: eg. 192.168.0.10:21

Port numbers are assigned by the IANA (Internet Assigned Numbers Authority)

There a 3 different types of port numbers :
Well known Ports (1 - 1023) - Used for common services such as FTP, HTTP, Telnet, DHCP.
Registered Ports (1024 - 49151) - Used for services that are not as commonly used that they warrant a well known port number. Eg. WAP, MS SQL, World of Warcraft.
Private/Dynamic Ports (49152 - 65535) - Ports that can be used by anyone for any purpose.

You can view ports that are currently being used on your PC by typing 'netstat' into the DOS prompt (as seen below a after colon in private/public address).

A common port number that you can see in the below display is the one at the bottom of my netstat display.
Windows has chosen to display it as 74.125.237.19:http but it could also be written as 74.125.237.19:80 which is the socket number.

Other common port numbers are: