An L2 policy based multipath fabric

Ethernet is the Layer 2 infrastructure of choice for modern data center networks and service provider metro networks. These networks need to scale to a high number of end hosts and bridges, provide isolation between tenants and support host mobility with an efficient bandwidth use and reduced operating costs. Ethernet uses controlled flooding of frames and the spanning tree protocol, falling short on demands like scalability and full usage of the topology. Solutions at Layer 3 solve some of the problems but they are harder to configure, more expensive and pose difficulties to host mobility. Recent efforts try to bring some of the advantages of L3 to L2 by using equal cost multipath (ECMP) control planes to populate the bridges forwarding tables. In this paper we go beyond and propose a non-ECMP solution where the paths are selected by policy. This means that very different paths (in terms of the physical topology) can be considered equal. It provides an extra layer of flexibility in traffic distribution with a high utilization of the network in a single L2 Ethernet domain. Our design is based on routing algebra theory and its correct behaviour can be proved for both centralized and distributed implementations.