Freeradius on Linux with dynamic VLAN assignment via AD

I've been trying to configure my freeradius server on Linux to authenticate users from an existing Active Directory (windows server 2003) and i've already done that. Now i need to assign VLANs to those users and i dont know how to :(. The logical procedure should be with an AD attribute but i haven't found which one nor how to read it from the AD to use it on the freeradius server… Can anyone help me with this or tell me where can i find a solution?

Thanks in advance