Windows NT 4.0 Service Pack 2 (SP2) provides support for a new DHCP
"superscope" feature. This feature allows a Windows NT DHCP server to:
- Support DHCP clients on locally attached networks that have multiple
logical subnets on one physical network (sometimes referred to as a
- Support DHCP clients on the far side of bootp relay agents, where the
network on the far side of the relay agent has multiple logical subnets
on one physical network.
Versions of Windows NT DHCP server prior to Windows NT 4.0 Service Pack 2
are not capable of assigning addresses from more than one scope to a given
physical subnet. One workaround for this situation is to add additional
network interface cards (NICs) to the server, and to address each of the
NICs to a given logical IP subnet. This involves additional and otherwise
unnecessary hardware, so a new solution was developed and implemented in
The enhanced DHCP server allows the administrator to create different
scopes (ranges of IP addresses), and then to group those scopes together
into a superscope.
To create a superscope, complete the following steps:
- Create each of the scopes using DHCP Manager. Assign global and scope
properties as desired. Be sure to enable each scope.
- In DHCP Manager, select the DHCP server. Click Scope, and then click
- Click Create Superscope, supply a name for the superscope, and then
- Add the appropriate scopes from the Available Scopes list to the Child
Sub-Scopes list. When finished, the Child Scopes should be listed from
top to bottom in the order that you want addresses to be used from them.
NOTE: The order that you add the Child Sub-Scopes is of no consequence.
DHCP Manager will sort them in ascending order.
- Click OK.
- If the DHCP server is configured with the IgnorebroadcastFlag DHCP
Registry value set to 0, and if the Superscope is on a subnet that is
directly attached to the server (that is, not being reached via a DHCP
relay agent), then each of the logical subnets must be directly
reachable by the DHCP server. This means that there must be a local
route to each logical subnet. The easiest way to accomplish this is to
add an IP address to the NIC on the local server for each of the logical
subnets that it is attached to.
For additional information about the IgnorebroadcastFlag DHCP Registry
value, see the following article in the Microsoft Knowledge Base:
TITLE : Configuring a Microsoft Windows NT 4.0 DHCP Server for
Article ID: 161571 - Last Review: November 1, 2006 - Revision: 1.1
- Microsoft Windows NT Server 4.0 Standard Edition