DHCP User Classes

DHCP User Classes allow you to apply additional DHCP options, or a modified set of options, to certain clients on your network as identified by a user class id. For example, you may want to define a different gateway, DNS servers, or lease time for a subset of the computers on your network. This can be accomplished by setting a user class id on those clients (2000 and above) and then configuring that class id appropriately on the local DHCP server.

If you have non-Microsoft DHCP clients, you can define other vendor-specific classes on the DHCP server.

http://www.techrepublic.com/article/use-dhcp-class-to-deny-internet-access-to-unauthorized-machines/5498436
http://blogs.technet.com/b/teamdhcp/archive/2006/07/18/442304.aspx

Managing User Classes:
 Applies To: Windows Server 2008 R2
"User classes allow DHCP clients to differentiate themselves by specifying a User Class option. When available for client use, this option includes a user-determined class ID that can help to group clients of similar configuration needs within a scope.  For example, you might support users and computers with mobile computing needs by configuring a user class at the DHCP server and setting the related class ID at the client computers."
 http://technet.microsoft.com/en-us/library/dd145308(v=ws.10).aspx
 
More About Predefined DHCP Options:
Applies To: Windows Server 2008 R2
http://technet.microsoft.com/en-us/library/dd759232.aspx 
 
Using option classes
http://technet.microsoft.com/en-us/library/cc775694(v=ws.10).aspx
 
How to Create a New DHCP User or Vendor Class
First configure the Option Class, then you set it at the client side, such as (quoted from the article):
 To Set the Specified DHCP Class ID String for Client Computers:
 Client computers that connect to a Windows 2000-based DHCP server can use the following command to set the specified DHCP class ID string:
 ipconfig /setclassid adapter_name class_id
 For example, to configure an adapter called "Local Area Connection" with a user class ID called "myuserclass", type ipconfig /setclassid Local Area

Connection myuserclass at a command prompt, and then press ENTER.
 http://support.microsoft.com/kb/240247
 
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Example step by step
 
Use DHCP Class to deny Internet access to unauthorized machines
 http://www.techrepublic.com/article/use-dhcp-class-to-deny-internet-access-to-unauthorized-machines/5498436

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