Abstract
The layer 2 network technology is extending beyond its traditional local area implementation and finding wider acceptance in provider’s metropolitan area networks and large-scale cloud data center networks. This is mainly due to its plug-and-play capability and native mobility support. Many efforts have been put to increase the bisection bandwidth in a layer 2 network, which has been constrained by the spanning tree protocol that a layer 2 network uses for preventing looping. The recent trend is to incorporate layer 3’s routing approach into a layer 2 network so that multiple paths can be used for forwarding traffic between any source-destination (S-D) node pair. ECMP (equal cost multipath) is one such example. However, ECMP may still be limited in generating multiple paths due to its shortest path (lowest cost) requirement. In this paper, we consider a non-shortest-path routing approach, called EPMP (Equal Preference Multi-Path) that can generate more paths than ECMP. The EPMP is based on the ordered semi-group algebra. In the EPMP routing, paths that differ in traditionally-defined costs, such as hops, bandwidth, etc., can be made equally preferred and thus become candidate paths. We found that, in comparison with ECMP, EPMP routing not only generates more paths, provides higher bisection bandwidth, but also allows bottleneck links in a hierarchical network to be identified when different traffic patterns are applied. EPMP is also versatile in that it can use various ways of path preference calculations to control the number and the length of paths, making it flexible (like policy-based routing) but also objective (like shortest path first routing) in calculating preferred paths.
Highlights
A layer 2 network by definition is a network where its protocol data units can be transported from source to destination by using a data-link layer (the second layer in the Open System Interconnection (OSI) layering model) protocol, without the need of a network layer protocol
We have investigated the Equal Path Multi-Path routing algorithm, which is a non-shortest path first (SPF) routing algorithm based on ordered semi-group preference algebra
We showed that its use in hierarchical networks, like the data center networks, provides several benefits
Summary
A layer 2 network by definition is a network where its protocol data units (or frames) can be transported from source to destination by using a data-link layer (the second layer in the Open System Interconnection (OSI) layering model) protocol, without the need of a network layer (the third layer in the OSI model) protocol. It disables some links for preventing loops, does not allow source-destination traffic to take multiple paths; with the tree structure, its paths are inefficient for paths that do not end in the root node; and it converges slowly to a new solution if a node or link fails Such characteristics are rather undesirable for provider networks or data center networks, where both ample bisection bandwidth and fast recovery are critical in their operations. IETF works on the TRILL (Transparent Interconnection of Lots of Links) [8] [9], where its Rbridges (Routing Bridges) runs on layer 2 with the help of the link state routing protocol (IS-IS) Both SPB and TRILL are emerging promising standards for provider networks and data center networks.
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