Using Scopes with Different Subnet Masks in a Superscope

Last reviewed: March 2, 1998
Article ID: Q169291

The information in this article applies to:

Microsoft Windows NT Server version 4.0

SYMPTOMS

When you use a superscope made up of scopes with different subnet masks, client computers may not be able to get an IP address using DHCP. This situation will occur if the first scope in the superscope is full.

Example

You have a single segment using the following addresses:

   192.168.1.1-255, subnet mask 255.255.255.0
   192.168.2.1-62, subnet mask 255.255.255.192

You use one DHCP server, create a scope for each network, and then create a superscope using these two scopes. This procedure will allow your DHCP server to assign addresses from either scope to clients on the same physical segment.

After the 192.168.1.0 scope is full, a client can no longer get an IP address using DHCP. If you look at the event viewer log on your computer running Windows NT DHCP server, you will see that the server sent a NACK to itself for an address it just tried to give out.

RESOLUTION

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.

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.

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

For more information about the NACKing behavior introduced in SP2, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q163055
   TITLE     : DHCP Client May Fail with NT 4.0 SP2 Multinetted DHCP Server

Keywords          : NTSrv nttcp kbbuglist kbnetwork
Version           : 4.00
Platform          : winnt
Issue type        : kbbug
Solution Type     : kbservicepack

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Last reviewed: March 2, 1998
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