TCP/IP for Beginners - IP Addressing and DHCP

Users obtain an IP address when they connect to a network. Although it may seem magical, it is a process that takes place when your computer boots into its operating system.

During the boot process, your computer calls out in search of a DHCP server. (DHCP is Dynamic Host Control Protocol.) The DHCP server comes in many forms. The server can be a Windows Server such as Windows 2003 Server or Windows 2008 Server. The server can also be a firewall that has DHCP capabilities or a router that has DHCP capabilities.

The DHCP process is simple. The DHCP device (server, firewall or router) listens for requests. In simplest terms, when your computer boots, it says, "I need a number!" The DHCP device looks to see what numbers are available in its pool of numbers. (Home routers are generally setup with 192.168.x.x numbers.) This pool of numbers is like a license to travel the network. Any computer requesting a number is given one for a period of time. This time frame is called 'lease time'. Your computer can have this number for this time and the server will not give this number to another computer. If the computer doesn't use this number, the number is placed back in the pool of numbers for other computers to use. The number is generally yours as long as you use the computer in this time frame.

If a DHCP server is not available, you may get an APIPA (Automatic Private IP Addressing) number. This number is in the 169 series of numbers. If you are issued this number (by your own operating system), it means the server could not be contacted. This number will not allow you to communicate over the internet. You will only be able to communicate with computers with the same series of numbers. We will cover troubleshooting in the part of this series.

Generally DSL and Cable providers give you one IP address if you connect to their routers directly. Users who use DSL or Cable who have more than one computer must buy a router. The router will have a WAN connection that connects to the DSL or Cable connection. The router acts as a mini DHCP server through its ports on the back or the wireless (if wireless capable) connection it may have. Generally these routers support 20 to 50 computers. The router uses NAT (Network Address Translation) to negotiate the broadband connection. The DSL or Cable modem only 'sees' one device connected to it. The router basically splits this one connection into many.

In the next part, we will examine troubleshooting the TCP/IP protocol.

Many small and large companies may use a DHCP server to process their IP addresses. DHCP Servers give the IP address, subnet, gateway, and DNS numbers to computers requesting an IP. The servers have a static number (that never changes) in the IP address range the system administrators decide on. Administrators base the IP address scheme on the number of computers they are servicing. This is based on the charts found in the first and second parts of this series.