Page Comparison

...

The NIOS appliance can filter DHCP address requests by user class filters. A user class indicates a category of user, application, or device of which the DHCP client is a member. User class identifiers are configured on DHCP clients and are sent during a DHCP address request operation. The client includes the user class identifier in DHCP option 77 when sending DHCPDISCOVER and DHCPREQUEST messages.
By using user class identifiers, a DHCP server can screen address requests and assign addresses from select address ranges based on the different user class identifiers it receives. For example, if you assign a user class filter named mobile to a range of addresses from 10.1.1.31–10.1.1.80, the appliance selects an address from that range if it receives an address request that includes the user class name mobile and there are still addresses available in that range. You might want mobile users to receive these addresses because you have given them shorter lease times than other, more stationary DHCP clients. See Figure 31.6.

If the NIOS appliance receives address requests with the user class mobile and there are no available addresses in address range 2 but there are available addresses in ranges 1 and 3, the appliance begins assigning addresses from address range 3 (because its addresses are higher than those in range 1). Then, if all addresses in range 3 are in use, the appliance begins assigning addresses from address range 1. If you want the appliance to assign addresses to mobile users (that is, those identified with the user class mobile) exclusively from address range 2, then you must apply user class filters for "mobile" to address ranges 1 and 3 that deny lease requests matching that user class.

...