Microsoft KB Archive/255836

= Change in DHCP Client Behavior in Windows 2000 =

Article ID: 255836

Article Last Modified on 3/3/2007

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APPLIES TO


 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows 2000 Professional Edition

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This article was previously published under Q255836



SYMPTOMS
A Windows 2000 client may lose connectivity to all network resources if it receives its IP configuration by using Dynamic Host Configuration Protocol (DHCP). Earlier-version clients that use DHCP may still have access to network resources.



CAUSE
A Windows 2000-based DHCP client may lose connectivity to local network resources if it is unable to reach a DHCP server at startup. Windows 2000 behaves differently than does previous versions of Windows when it is unable to find a DHCP server. The Windows 2000-based DHCP client may use Automatic Private IP Addressing (APIPA) for addressing if it is unable to reach a DHCP server and is also unable to reach its default gateway. After the APIPA address is enabled, the client loses connectivity to other local network resources. Previous versions of Windows continue to use the currently leased DHCP address until the lease expires.

To determine whether a Windows 2000-based DHCP client has used APIPA for TCP/IP addressing, type ipconfig at a command prompt, and then press ENTER. If APIPA was used, the IP address is from the APIPA Class B range of 169.254.0.0 to 169.254.255.255.

The client computer continues to search for a DHCP server and leases its previous address or a new address when a DHCP server becomes available.



RESOLUTION
To work around this behavior, you can disable APIPA either on the entire computer or on a per-interface basis. If you choose to disable APIPA, you need to modify the registry. For additional information about how to do this, click the article number below to view the article in the Microsoft Knowledge Base:

244268 Routing Does Not Work When Multiple Adapters Use Automatic Private IP Addressing Simultaneously



STATUS
This behavior is by design.



MORE INFORMATION
A capture of network traffic shows that the Windows 2000-based client sends DHCP discover packets, and then attempts to ARP for the address of the default gateway. If the default gateway is unreachable, the client grants itself an address by using APIPA while periodically sending DHCP discover packets. When connectivity to the DHCP server is restored, the client attempts to obtain its previous address.

Additional query words: autonet autoip

Keywords: kbdhcp kbprb KB255836

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