Microsoft KB Archive/169122

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Non-rfc Compliant DHCP Server Does Not Send DHCPNAK When Client is Moved to Another Subnet

Article ID: 169122

Article Last Modified on 11/1/2006


  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Server 4.0 Standard Edition

This article was previously published under Q169122


When a Windows NT DHCP client is moved to another subnet (without issuing the ipconfig/release command before moving), the client will request its previous IP address. Usually this IP address is not valid for usage on the new subnet.

When a DHCP server detects that the client requests an IP address that does not fit for the current subnet, the DHCP server must send a DHCPNAK to the client (according to RFC1541).

Some non-rfc compliant DHCP servers do not send this DHCPNAK. Because of this, the client does not attempt to lease a new IP address on the new subnet and tries to use its old IP address (see the frame information later in this article).

This problem has been experienced only when using a third-party DHCP server. The Microsoft Windows NT DHCP server does not experience this behavior.


Per RFC1541, a DHCP server sends a DHCPNAK to a client that requests an IP address but is not located on the current subnet. According to RFC1541 (page 28):

In particular, if the previously allocated network address in the ciaddr field from the client does not match the network address recorded by the server for that client, the server sends a DHCPNAK to the client.

After receiving a DHCPNAK, the DHCP client will restart the DHCP lease process by sending DHCPDISCOVER.


Contact the non-rfc compliant DHCP server vendor for assistance or use the Microsoft Windows NT DHCP server.

Additional query words: SRD970304000093

Keywords: kb3rdparty kbnetwork KB169122