TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. - TechTarget
In our opinion, understanding TCP/IP is the MOST important technical security skill. Networking, software, hacking skills ALL rely on communications. Software applications, databases, and operating systems ALL have to communicate in order to create an information system.
TCP/IP is the most common and widely used means to communication over an internet, intranet, or extranet. Understanding how that works is key to proper security for your system.
Read this article to learn more about TCP/IP.
Want to know what some of the common ports like HTTP, SSL, or SSH? Read this article.