IETF RFC 6575 PDF

The Virtual Private Wire Service (VPWS), detailed in RFC 4664, provides point-to-point connections between pairs of Customer Edge (CE) devices. It does so by binding two Attachment Circuits (each connecting a CE device with a Provider Edge (PE) device) to a pseudowire (connecting the two PEs). In general, the Attachment Circuits must be of the same technology (e.g., both Ethernet or both ATM), and the pseudowire must carry the frames of that technology. However, if it is known that the frames' payload consists solely of IP datagrams, it is possible to provide a point-to-point connection in which the pseudowire connects Attachment Circuits of different technologies. This requires the PEs to perform a function known as "Address Resolution Protocol (ARP) Mediation". ARP Mediation refers to the process of resolving Layer 2 addresses when different resolution protocols are used on either Attachment Circuit. The methods described in this document are applicable even when the CEs run a routing protocol between them, as long as the routing protocol runs over IP.