Mastering TCP/IP Part 1: Application Layer – CompTIA Security+ Lesson 5

A quick introduction to TCP/IP. We are going to look how it’s built, the application layers and the protocols used in it.

We all should be familiar with the term TCP/IP by now. You can go google it or check it out on wikipedia if you don’t know what it is. But to summarize a bit from wikipedia:

The Internet protocol suite provides end-to-end data communication specifying how data should be packetized, addressed, transmitted, routed and received. This functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved.
Wikipedia, 8. Feb. 17


Since TCP/IP precedes the creation of the 7- layers OSI model it has just 4 layers. They have unique functions and methods for accomplishing work. With own rules and capabilities. The picture shows the model for UDP/IP, which is the same, except for the UDP.

Application Layer

The Application Layer allows appliactions to access services or protocols to exchange data. Most programs use this layer. The most used protocols in this layers are (you might know most of them if you ever worked in with networks or in software dev):


Name Short Description Default Port URL
Hypertey Transfer Protocol HTTP Used for the web. Applications use HTML 80 http://
HTTP Secure HTTPS Used for transmitting secure data over HTTP. Combines HTTP and SSL/TLS to provide encrypted communication. 443 https://
File Transfer Protocol FTP Used for File uploads and downloads from and to hosts on the internet. Various versions are available of it:

  • FTP
  • FTPS: FTP over SSL
 20, 21
Simple Mail Transfer Protocol SMTP Standard protocol for email communications 25
Telnet Telnet Interactive terminal emulation protocol. Allows remote user to conduct an interactive session with a Telnet server, which can appear as a local one to the client. 23
Domain Name System DNS Allows hosts to resolve hostnames to an IP- address 53
Remote Desktop Protocol RDP Allows Windows-based machines to be used by another Windows-based machine in the network. 3389
Simple Network Management Protocol SNMP Allows communications between network devices and management consoles. Mostly used by routers, bridges and intelligent hubs 161
Post Office Protocol POP Used for receiving email. Most commonly known as POP3 (the 3rd version). Many systems use IMAP (port 143). The difference was that POP was not designed to keep your mail on the server, while IMAP was. But knwadays you can configure POP to keep the mails on the server.. 110

Stay tuned for the next part: Transport, Internet and Network Access Layer.