3. Requirements

DLEP MUST be implemented on a single Layer 2 domain. The protocol identifies next-hop destinations by using the MAC address for delivering data traffic. No manipulation or substitution is performed; the MAC address supplied in all DLEP Messages is used as the Destination MAC address for frames emitted by the participating router. MAC addresses MUST be unique within the context of the router-modem session.

To enforce the single Layer 2 domain, implementations MUST support the Generalized TTL Security Mechanism [RFC5082], and implementations MUST adhere to this specification for all DLEP Messages.

DLEP specifies UDP multicast for single-hop discovery signaling and TCP for transport of the Messages. Modems and routers participating in DLEP sessions MUST have topologically consistent IP addresses assigned. It is RECOMMENDED that DLEP implementations utilize IPv6 link-local addresses to reduce the administrative burden of address assignment.

DLEP relies on the guaranteed delivery of its Messages between router and modem, once the 1-hop discovery process is complete -- hence, the specification of TCP to carry the Messages. Other reliable transports for the protocol are possible but are outside the scope of this document.