DHCP Server Fails to Lease Addresses for New Scope

It may be necessary to remove an existing scope from a Dynamic Host Configuration Protocol (DHCP) server and replace it with a new scope. For example, you may obtain a registered class of IP addresses for your network or you may be changing the class of IP addresses to accommodate more hosts or networks. This article discusses the recommended method of performing this task.

When you need to change your DHCP scope range, it may be necessary to leave the server's original IP address bound to the network interface card (NIC) for connectivity reasons until all clients have obtained an IP address from the new scope. However, if you just create the new scope, you may notice that the DHCP server does not assign leases from the newly created scope(s) after binding additional IP address(es) to the NIC.

This can happen because DHCP only binds to one IP address for each NIC and this IP address is the primary address found in TCP/IP properties. The additional addresses are found in the Advanced Properties of TCP/IP dialog box.

To make this transition, you will need to do one of the following:

• Change the primary IP address on the NIC to an IP address that is a part of the same network as the new scope.
  
  NOTE: This is the only option if you have Windows NT Server version 3.51 or Windows NT Server version 4.0 before Service Pack 2.
  
  -or-
• Configure the server to use a Superscope that includes the old scope(s) and the new scope(s).
  
  For additional information, please see the following article in the Microsoft Knowledge Base:
  
  ARTICLE-ID: 161571  (http://support.microsoft.com/kb/161571/EN-US/ )
  TITLE : Using DHCP "Superscopes" to Serve Multiple Logical Subnets

NOTE: If you cannot change the primary IP address of your NIC and you must use the second option above, leave the original scope active and exclude all the addresses within the scope.