The primary difference between TCP and UDP is that TCP is connection-oriented and UDP is connectionless.

In the TCP/IP protocol stack, messages associated with the common application protocols that most of us are familiar with such as HTTP for the Web SMTP, POP, and IMAP for e-mail Telnet and SSH for remote logon and FTP for file transfers operate over the Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) TCP and UDP messages, in turn, are carried inside Internet Protocol (IP) packets. If you don't know what a port scanner is, you should and if you don't use a port scanner to test your defenses, you should. Originally only available for Unix/Linux systems and distributed on underground hacker web sites, port scanners are now also available for Windows platforms and have even entered the realm of reputable, commercial software. Port scanning software has long been in the hacker's arsenal and is finally emerging as an important defensive tool as well. This is where port scanners come in with this tool, a system, network, or security administrator can check a group of hosts all at once. But running this command means actually walking or remotely accessing each and every server and you miss other host systems that might be listening on improper ports. The most common host-based tool for checking for open ports on Windows or Unix systems is the netstat command. In some cases, the services might be Trojans just waiting to be exploited. System administrators are constantly being advised to check their systems for open ports and services that might be running that are either unintended or unnecessary. Port Scanning: It's Not Just an Offensive Tool AnymoreĪn edited version of this paper with the title 'Plugging Leaky Holes' originally appeared in the June 2001 issue of Information Security Magazine ( Copyright © 2001.

Check linux port usage