Using Scopes with Different Subnet Masks in a Superscope (169291)

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 Dynamic Host Configuration Protocol (DHCP). This situation occurs 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

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

152734 How to Obtain the Latest Windows NT 4.0 Service Pack

STATUS

Microsoft has confirmed that this is a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.

MORE INFORMATION

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

161571 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:

163055 DHCP Client May Fail with NT 4.0 SP2 Multinetted DHCP Server