TCP/IP

By Joshua Erdman
Digital Foundation, inc.

TCP/IP is a network protocol (other network protocols include netBEUI, IPX/SPX, and Appletalk). To understand network protocols in gerneral, I highly recommend our article on the
7-layer OSI reference Model.

TCP/IP Background

In the 90's before the Internet was extremely popular, networking protocols varied. Typically the computers and operating systems that were a majority determined the protocol that was used. An office with Macs would use AppleTalk, an office with a Netware server would run IPX/SPX. Now that the Internet plays a HUGE role, today in almost all forms of business the main protocol used is TCP/IP.

TCP/IP Basics

Addressing

An IP address is made up of 4 numbers ranging from 0 - 255, each number being separated by a period (ex. 192.168.0.3). For a computer to participate on a TCP/IP network, it must be assigned an IP address unique from all other computers on its local network.

For much more detailed information, please read our article on TCP/IP addressing.

TCP/IP Ports

The Addressing scheme ensures that the data arrives at the intended destination, but it is the TCP/IP ports that help define what service or purpose the traffic is for. For example e-mail (SMTP) is port 25, web browsing (HTTP) is port 80 and for Secure web browsing (HTTPS) it is port 443. Each network service will use its own port, many of these ports are standard and assigned, these assigned ports are in the range from port 1 to 1023. Network services and programs without an official assignment (such as network games and file swapping programs) use ports scattered throughout the rest of the port range (1024 - 65,5535).

Common Ports

The most common ports include:

20;21 - FTP
22 - SSH
23 - Telnet
25 - SMTP
80 - HTTP
110 - POP3
143 - IMAP
443 - HTTPS
1701 - L2TP (UDP) - not compatible with NAT
1723 - PPTP (TCP)
3389 - MS Remote Desktop/Terminal Services
5631 & 5632 - pcAnywhere

For a complete list of IP Ports, please refer to: TCP/IP Port Reference.

CLUE: To better understand ports, think of your house as being the computer. The mailing address of your house is like your computer's IP address. The TCP/IP ports for your computer are like the different ways your house is accessed, such as your front door for people, water and gas pipes and power lines for your utility sservices. Each of these can be thought of as a port.

References:
TCP/IP Addressing

MAC Addresses

7-layer OSI Reference Model

Article last reviewed: 10/09/2006

Created by: Digital Foundation, inc.

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