RADIUS Attribute: NAS-Port what is the true Length?

Hello List, Probably not the right place to ask but I would like to know if someone could explain to me the following: According to RFC2138, the maximum range for the NAS-Port is 16 bits, so with the Type and Length fields to total length is 6 octets. But with FreeRadius's SQL Schema the NAS-PortId field is a varchar(15) and I see it being used. The dictionary.rfc2138 just states it is an integer so what is the maximum range on the NAS-Port field? If it has been changed, could someone point me to the correct RFC. -- Kind Regards Etienne Pretorius