http://www.rfc-editor.org/rfc/rfc4580.txt
RFC 4580: Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Relay Agent Subscriber-ID Option, B. Volz2006-06-01T23:00:00-00:00This memo defines a new Relay Agent Subscriber-ID option for the Dynamic Host Configuration Protocol for IPv6 (DHCPv6). The option allows a DHCPv6 relay agent to associate a stable "Subscriber-ID" with DHCPv6 client messages in a way that is independent of the client and of the underlying physical network infrastructure. [STANDARDS-TRACK]