Monday, October 22, 2012

How to fix IP address 169.254.x.x no conectivity

Understanding DHCP

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 169.254.x.x 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.

This article describes how to use automatic Transmission Control Protocol/Internet Protocol (TCP/IP) addressing without a Dynamic Host Configuration Protocol (DHCP) server being present on the network. The operating system versions listed in the "Applies to" section of this article have a feature called Automatic Private IP Addressing (APIPA). With this feature, a Windows computer can assign itself an Internet Protocol (IP) address in the event that a DHCP server is not available or does not exist on the network. This feature makes configuring and supporting a small Local Area Network (LAN) running TCP/IP less difficult.

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