SPAIN: COTS Data-Center Ethernet for Multipathing over Arbitrary Topologies
Abstract
Operators of data centers want a scalable network fabric that supports high bisection bandwidth and host mobility, but which costs very little to purchase and administer. Ethernet almost solves the problem – it is cheap and
supports high link bandwidths – but traditional Ethernet
does not scale, because its spanning-tree topology forces
traffic onto a single tree. Many researchers have described “scalable Ethernet” designs to solve the scaling
problem, by enabling the use of multiple paths through
the network. However, most such designs require specific wiring topologies, which can create deployment
problems, or changes to the network switches, which
could obviate the commodity pricing of these parts.
In this paper, we describe SPAIN (“Smart Path Assignment In Networks”). SPAIN provides multipath forwarding using inexpensive, commodity off-the-shelf (COTS)
Ethernet switches, over arbitrary topologies. SPAIN precomputes a set of paths that exploit the redundancy in a
given network topology, then merges these paths into a
set of trees; each tree is mapped as a separate VLAN
onto the physical Ethernet. SPAIN requires only minor end-host software modifications, including a simple algorithm that chooses between pre-installed paths
to efficiently spread load over the network. We demonstrate SPAIN’s ability to improve bisection bandwidth
over both simulated and experimental data-center networks.