Automatic Windows 98 TCP/IP Addressing Without a DHCP Server

ID: Q220874

The information in this article applies to:
IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

SUMMARY

This article describes how to use Windows 98 automatic Transmission Control Protocol/Internet Protocol (TCP/IP) addressing without a Dynamic Host Configuration Protocol (DHCP) server being present on the network. Windows 98 has a feature called Automatic Private IP Addressing (APIPA). With this feature, a Windows 98 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.


MORE INFORMATION

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys and Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).

A Windows 98-based computer that is configured to use DHCP can automatically assign itself an Internet Protocol (IP) address if a DHCP server is not available. For example, this could occur on a network without a DHCP server, or on a network if a DHCP server is temporarily unavailable. The IP address assigned through APIPA comes from a pool of private, internal IP addresses that are not valid for computers that are participating on the Internet. The addresses are in the Class B IP address range, and hosts are assigned an IP address from the following network address range:

169.254.3-digit number.3-digit number
where 3-digit number is a 3-digit number. After the network adapter has been assigned an IP address, the computer can use TCP/IP to communicate with any other computer that is connected to the same LAN and that is also configured for APIPA or has the IP address manually set to the 169.254.3-digit number.3-digit number address range with a subnet mask of 255.255.0.0. Note that the computer cannot communicate with computers on other subnets, or with computers that do not use automatic private IP addressing. Automatic private IP addressing is enabled by default. You may want to disable it in any of the following cases: Unless you have disabled DHCP-related messages, DHCP messages provide you with notification when you change between DHCP addressing and automatic private IP addressing. If DHCP messaging is accidentally disabled, you can turn the DHCP messages back on by changing the value of the PopupFlag value in the following registry key from 00 to 01:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\DHCP
Note that you must restart your computer for the change to take effect. You can also determine whether your computer is using automatic private IP addressing by using the Winipcfg tool: You can disable automatic private IP addressing by using either of the following methods:

Examples of Where APIPA May Be Useful

Example 1: No Previous IP Address and no DHCP Server

When your Windows 98-based computer (configured for DHCP) is initializing, it broadcasts three or more "discover" messages. If a DHCP server does not respond after several discover messages are broadcast, the Windows 98 computer assigns itself a Class B (APIPA) address. Then the Windows 98 computer will display an error message to the user of the computer (providing it has never been assigned and IP address from a DHCP server in the past). The Windows 98 computer will then send out a Discover message every three minutes in an attempt to establish communications with a DHCP server.

Example 2: Previous IP Address and no DHCP Server

The computer checks for the DHCP server and if none are found, an attempt is made to contact the default gateway. If the default gateway replies, then the Windows 98 computer retains the previously-leased IP address. However, if the computer does not receive a response from the default gateway or if none are assigned, then it uses the automatic private IP addressing feature to assign itself an IP address. An error message is presented to the user and discover messages are transmitted every 3 minutes. Once a DHCP server comes on line, a message is generated stating communications have been re-established with a DHCP Server.

Example 3: Lease Expires and no DHCP Server

The Windows 98-based computer tries to re-establish the lease of the IP address. If the Windows 98 computer does not find a DCHP server, it assigns itself an IP address after generating an error message. The computer then broadcasts a discover message every 3 minutes until a DHCP server comes on line. A message is then generated stating that communications have been re-established with the DHCP Server.

Additional query words: autonet 


Keywords          : kbnetwork kbtool win98 
Version           : WINDOWS:
Platform          : WINDOWS 
Issue type        : kbhowto

Last Reviewed: July 21, 1999