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Tech Tips / Windows NT / Networking

Port numbers?

Ever wondered what a port number is and where it comes from? In a TCP/IP-based network such as the Internet, port numbers are assigned to application programs running in the computer. They're used to connect incoming data to the appropriate services.

Well-known ports (those from 0 through 1023) are standard port numbers everyone uses. For example, port 80 is used for HTTP traffic (Web traffic). The Internet Assigned Numbers Authority (IANA) assigns well-known port numbers.

Then, there are registered ports and dynamic and/or private ports. Windows NT is most susceptible to attacks using these ports.

Other commonly used ports and their numbers include:

• FTP - Port 20/21
• SMTP - Port 25
• Telnet - Port 23

For more information on port numbers, see Microsoft Knowledge Base article Q174904. For a complete list of port numbers, check out the IANA's Web site.