Rapid depletion of the available IPv4 address space was the main initiator of IPv6. In consequence, the demand to never again have to develop a new protocol due to the lack of addresses was one of the principal requirements to the new address space design. Let’s look how it was fulfilled. The basic rules of IPv6 addressing are laid down by RFC 3513 [RFC3513]. Some accompanying RFCs define the specialties and rules for specific address types.