Freeradius Restrict User Auth Request Based on VLAN

Scenario: We have Mikrotik as NAS and Freeradius as billing. VLAN are configured for each dealer's area. We have few reseller/franchise managers, like Dealer-A, Dealer-B. They can create there own users in freeradius using fronted designed in php. All dealers can view/edit there own users only. Sometimes it happens that Dealer-A creates ID and give it to a user/friend who is sitting in Dealer-B network, therefore from Billing perspective its a Loss of Dealer-B. Can we impose some restriction so that User-ID's created by each dealer should be able to connect only from his network (or from there own VLAN) only. Regards, JZ <http:///>