DHCP Clients' Ability to Send DHCPDECLINE Message

• Microsoft Windows NT Workstation version 4.0
• Microsoft Windows NT Server version 4.0

SUMMARY

In the current implementation of the Microsoft dynamic host configuration protocol (DHCP) service, if a device is provided with an Internet Provider (IP) configuration by way of DHCP, we do a courtesy Address Resolution Protocol (ARP) with the provided IP address. If anyone responds, that means the address is in use. In this case, when a duplicate IP is detected as the TCP/IP protocol tries to initialize, a popup message is provided to the user stating that a duplicate IP address exists. The user is informed to get system administration assistance. At that point, the TCP/IP protocol initialization is failed and the user can't access any network resources.

MORE INFORMATION

DHCP RFC 1541 permits that instead of informing the user, initiating a manual process, a DHCP_DECLINE transaction can be returned to the DHCP server. The server will then allocate a different IP address for the device.

DHCP RFC 1541 indicates that it is the responsibility of the DHCP client to notify the DHCP server with a DHCP_DECLINE transaction if the client determines that there is a problem with the DHCP parameters provided by the DHCP Server.

The RFC states:

3.1 Client-server interaction - allocating a network address:

   The client receives the DHCPACK message with configuration parameters.
   The client performs a final check on the parameters and notes the
   duration of the lease and of the lease identification cookie specified
   in the DHCPACK message. At this point, the client is configured. If the
   client detects a problem with the parameters in the DHCPACK message, the
   client sends a DHCPDECLINE message to the server and restarts the
   configuration process. The client should wait a minimum of ten seconds
   before restarting the configuration process to avoid excessive network
   traffic in case of looping.

   If the server receives a DHCPDECLINE message, the client has discovered
   through some other means that the suggested network address is already
   in use. The server MUST mark the network address as "not allocated" and
   SHOULD notify the local system administrator of a possible configuration
   problem.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. This problem was corrected in the latest US Service Pack for Windows NT. For information on obtaining this update, query on the following word in the Microsoft Knowledge Base (without the spaces):

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