The DHCP server should support multiple Appliance Classes. Appliance class is not vendor specific. Multiple vendors may use the same appliance class identifier. The DHCP Client does not need to be a priori configured to know which subnet it is intended to reside on. Appliance class is not user definable and does not identify a class of users.
Appliances can only have one appliance class.
Servers supporting appliance class must echo the appliance class identifier on the DHCP Offer and DHCP ACK messages. DHCP servers must allow address pool selection based on matching appliance class criteria. The DHCP server may relay individual DHCP requests to specific DHCP server based on Appliance Class without effecting whether other requests are relayed. The Appliance Class Identifier is used by the DHCP Client to optionally identify the appliance class it represents. This option carries only one Appliance Class Identifier.