Description of Automatic Private IP Addressing in Windows Millennium Edition

This article provides a description of the Automatic Private IP Addressing feature in Windows Millennium Edition (Me).

In Windows Me, you can use the Automatic Private IP Addressing feature of Transmission Control Protocol/Internet Protocol (TCP/IP) to assign a unique Internet protocol (IP) address to a network adapter. This may be useful if you have a small network that does not have a DHCP server. With automatic private IP addressing, you can assign a unique IP address to your network adapter by using the LINKLOCAL network IP address space. LINKLOCAL network addresses always begin with the numbers 169.254 and have the following format: LINKLOCAL network addresses are used only for private, internal addresses, and are not valid for host computers that are "visible" on the Internet. They cannot be used for computers that are linked by Internet Connection Sharing (ICS).

After the network adapter is assigned a LINKLOCAL network IP address, computers can communicate (by using TCP/IP) with any other computer on the network that uses the same addressing.

A Windows computer that is configured to use automatic private IP addressing can assign itself a private IP address under the following conditions:

• If the computer is not configured as a portable computer, it can assign itself an automatic IP address at startup if the computer does not have a valid DHCP lease and no DHCP server is found on the network.
• If the computer is configured as a portable computer, it can assign itself an automatic IP address if no DHCP server is found on the network, regardless of whether it has a DHCP lease.

With automatic IP addressing, the IP address can be configured automatically. This method decreases administration time and means that IP addresses can be reused. Also, this method is recommended for all sizes of networks that do not have a direct Internet connection or available DHCP service.

Notes

If a DHCP service is later found, the computer stops using the automatic IP address, and instead uses the IP address that is assigned by the service. A DHCP IP address will not override a static IP address, and it must be changed manually. If a computer is moved from a local area network (LAN) with a DHCP service to a LAN without a DHCP service, you can use the IP configuration utility (Winipcfg.exe) to release the assigned DHCP address. You can then have the computer automatically assign a private IP address. Static IP addressing enables you to manually type a permanent IP address. Using this method is not recommended except as a last resort.