DHCP Client May Fail with WinNT 4.0 SP2 Multinetted DHCP Server

Last reviewed: March 2, 1998
Article ID: Q163055

The information in this article applies to:

Microsoft Windows NT Server version 4.0

SYMPTOMS

A DHCP client may fail to obtain a DHCP lease if multiple logical subnets exist and there is a Windows NT 4.0 Service Pack 2 (SP2) DHCP server on the network. Also, you may receive the following error message when you run the IPCONFIG /RENEW command:

   Access Denied - Renewing Adapter "xxxx"

Prior to Service Pack 2, when multiple logical subnets existed, the DHCP client was able to receive the DHCPOFFER and send a DHCPREQUEST to the offering DHCP server. After applying Service Pack 2, the DHCP servers on other logical subnets issue a DHCPNACK, which forces the client to release the address and perform a DHCPDISCOVER again.

In addition to the above error message, you may receive the following event log messages:

On the Client

   Event ID: 1006
   Source: Dhcp
   Type: Warning
   Category: None
   Description: DHCP service is shutting down. The following error
                occurred: Access is denied.

On the Server

   Event ID: 1011
   Source: DhcpServer
   Type: Warning
   Category: None
   Description: The DHCP server issued a NACK to the client (MAC Address of
                the Requesting Client) for the address (Requested IP
                Address) request.

CAUSE

Windows NT 4.0 SP2 DHCP servers issue a DHCPNACK to any DHCPREQUEST that does not appear to be valid for the subnet. This problem occurs when you are using multiple logical IP subnets (multinetting) and two DHCP servers on the same physical network are serving two different logical subnets.

For example, a client broadcasts DHCPREQUEST and receives ACK from server A and NACK from server B. Because there is no communication between server B and server A, server B is not aware of the existence of server A. If it does not send a NACK, then a client who has just moved to this network will never know that its old address is invalid.

RESOLUTION

To resolve this issue, obtain the following fix or wait for the next Windows NT service pack.

This fix should have the following timestamp:

   06/20/97  07:33 PM               116,496 Dhcpssvc.dll (Intel)
   06/20/97  06:32 PM               185,104 Dhcpssvc.dll (Alpha)

NOTE: Service Pack 3 must be applied to Windows NT 4.0 prior to applying this fix.

To workaround this issue, use one of the following:

Windows NT 4.0 SP2 includes the ability to create DHCP superscopes. After creating a scope and defining each logical subnet in a superscope, the DHCP server recognizes the DHCPREQUEST as valid and will not NACK the request.
For example, you have a multinet environment with the following DHCP servers on a single LAN:
```
      192.168.10.1
      192.168.20.1
      192.168.30.1
```
On each DHCP server you must create a superscope with a minimum of one IP address from each of the 10.x, 20.x and 30.x scopes. Be sure not to duplicate IP addresses in the scopes.
-or-
Another possibility is to take advantage of the superscoping feature and create one DHCP server to serve all scopes.

For more information on superscopes, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q161571
   TITLE     : Using DHCP "Superscopes" to Serve Multiple Logical Subnets

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. A supported fix is now available, but has not been fully regression-tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.

Additional query words: 4.00 prodnt sp2 multinet
Keywords : NTSrv nttcp kbnetwork
Version : 4.0
Platform : winnt

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Last reviewed: March 2, 1998
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