http://www.rfc-editor.org/rfc/rfc3993.txt
RFC 3993: Subscriber-ID Suboption for the Dynamic Host Configuration Protocol (DHCP) Relay Agent Option, R. Johnson, T. Palaniappan, M. Stapp2005-03-01T23:00:00-00:00This memo defines a new Subscriber-ID suboption for the Dynamic Host Configuration Protocol's (DHCP) relay agent information option. The suboption allows a DHCP relay agent to associate a stable "Subscriber-ID" with DHCP client messages in a way that is independent of the client and of the underlying physical network infrastructure. [STANDARDS-TRACK]