Commonly used TCP/IP ports and how they are used

When your web browser or email program connects to another computer on the Internet, it does so through a TCP/IP port. If you have a web server or FTP server running on your PC, it opens a port through which other computers can connect to those services. Port numbers are used to distinguish one network service from another.

Mostly, this is done behind the scenes. However, knowing which programs use a specific port number becomes important when you starting considering security. A firewall uses ports to form its rules about which types of network traffic to allow, and which to prohibit. And the Active Connections utility (netstat.exe), used to determine which ports are currently in use, allows you to uncover vulnerabilities in your system using ports.

Some firewalls make a distinction between TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) ports, which is typically unnecessary. In most cases, programs that use the more common TCP protocol will use the same port numbers as their counterparts that use the lessreliable UDP protocol.

Ports are divided into three ranges:
Well-known ports: 0–1023
Registered ports: 1024–49151
Dynamic and/or private ports: 49152–65535

Those ports marked with an × are commonly exploited by worms and other types of remote attacks. Unless you specifically need them, you should block them in your firewall or router.

Tags: dhcp,virtual,security

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