DOCUMENT:Q161571  09-AUG-2001  [winnt]
TITLE   :Using DHCP "Superscopes" to Serve Multiple Logical Subnets
PRODUCT :Microsoft Windows NT
PROD/VER:4.0
OPER/SYS:
KEYWORDS:kbnetwork

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The information in this article applies to:

 - Microsoft Windows NT Server version 4.0 
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SUMMARY
=======

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 "multi-net").

 - 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.

MORE INFORMATION
================

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 SP2.

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:

1. Create each of the scopes using DHCP Manager. Assign global and scope
   properties as desired. Be sure to enable each scope.

2. In DHCP Manager, select the DHCP server. Click Scope, and then click
   Superscopes.

3. Click Create Superscope, supply a name for the superscope, and then click OK.

4. 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.

5. Click OK.

6. 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:

   ARTICLE-ID: Q161429
   TITLE : Configuring a Microsoft Windows NT 4.0 DHCP Server for Unicast

Additional query words: multinet multihomed logical subnet scope superscope relay agent super
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Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400
Version           : 4.0

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