KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q161571: Using DHCP "Superscopes" to Serve Multiple Logical Subnets

Article: Q161571
Product(s): Microsoft Windows NT
Version(s): 4.0
Operating System(s): 
Keyword(s): kbnetwork
Last Modified: 09-AUG-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows NT Server version 4.0 
-------------------------------------------------------------------------------

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
======================================================================
Keywords          : kbnetwork 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400
Version           : 4.0

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.