L2TPv3 revision notes – architecture

L2TPv3 has been designed to transport layer-2 frames of various types over a layer-3 backbone.  Some aspects of the configuration are similar to that of EoMPLS – just without the need to deploy MPLS!

Packets are tunneled across the layer-3 network completely transparently, such that the two devices appear to be connected together. In the case of ethernet tunneling, there is no learning of MAC addresses – what goes in one side, comes out the other. That includes CDP, Spanning Tree and so on.

DPT / RPR (802.17) revision notes

DPT and RPR (802.17) are both dual ring-topology networks, where the traffic in each ring rotates in different directions.  DPT seems to have come first, it then became a standard of the IEEE in 2004, albeit with a few limitations.  So Cisco support a kind of Cisco-proprietary RPR on some of their equipment (the ONS optical platforms) that they consider better.