ClubMED: Coordinated Multi-Exit Discriminator Strategies for Peering Carriers Stefano Secci a,b , Jean-Louis Rougier a , Achille Pattavina b , Fioravante Patrone c , Guido Maier b a Institut Telecom, Telecom ParisTech, LTCI CNRS, France. E-mail: {secci, rougier}@telecom-paristech.fr b Politecnico di Milano, Italy. E-mail: {secci, pattavina, maier}@elet.polimi.it c Universit` a di Genova, Italy. E-mail: patrone@diptem.unige.it Abstract—Inter-domain peering links represent nowadays the real bottleneck of the Internet. On peering links carriers may coordinate to efficiently balance the load, but the current practice is often based on an uncoordinated selfish routing supported by the peer relationship. We present a novel game theoretical routing framework to efficiently coordinate the routing on peering links while modelling the non-cooperative carrier behaviour. It relies on a collaborative use of the Multi-Exit Discriminator (MED) attribute of BGP, hence it is nicknamed ClubMED (Coordinated MED). The incentives are the minimization of carrier routing costs, the control of peering link congestions and peering route stability. For the ClubMED game, we define the Nash Equilibrium Multi-Path (NEMP) routing policy that shall be implemented upon Nash equilibria and Pareto-efficient profiles. Intra-domain Interior Gateway Protocol (IGP) weight optimizations are consistently integrated into the framework. We emulated the peering settlement between the Internet2 and the Geant2 networks, employing real datasets, comparing the ClubMED results to the current BGP practice. The results show that the global routing cost can be reduced of roughly 17%, that the peering link congestion can be avoided and that the stability of the routes can significantly be reinforced 1 . I. I NTRODUCTION The Internet backbone is composed of a few Autonomous Systems (ASs). To simplify, one may say it is composed of a few inter-continental carrier providers that provide transit connectivity to those regional providers the most part of customers and stub ASs are connected to. Some of the core ASs are “peers” when they agree on free reciprocal transit of their clients’ IP flows. Peering agreements are usually signed when ASs get mutual operational and economical benefits from peering. The Border Gateway Protocol (BGP) v.4 is the current inter-AS IP routing protocol. It includes criteria that allow implementing peering settlements. As a matter of fact, the inefficient way in which these criteria are currently used overstresses inter-peer routing and overloads the peering links. This is mainly due to the unpredictability of the aggregate IP flows and to the fact that the free transit over peering links re- leases an AS from following the peer’s routing preferences [1]. This yields to selfish routing while, instead, coordination schemes may improve the bilateral routing efficiency. In previous work about inter-carrier connection-oriented services [2], it sorted out that a form of cooperation among carriers is needed to overtake privacy, billing and monitoring 1 Work funded by the INCAS S.JRA of the EU IST Euro-NF Network of Excellence and the ICF I-GATE project of the Institut T´ el´ ecom, France. issues. In this paper we argue how, instead, for connection- less IP services - for which such issues are not present - cooperation is not necessary in that coordination is enough. In particular, we concentrate on the coordination issue for peering settlements to reduce congestions, routing cost and route deflections. In Sect. II we link recent ideas in the area that motivated this work. We rely on the MED BGP attribute as the natural medium to convey coordination data. In Sect. III we define the ClubMED (Coordinated MED) framework, in which efficient strategy profiles can be detected in a non-cooperative game modelling. We define an effective routing policy relying on the concepts of Nash equilibria and Pareto-efficiency. We explain how, within the ClubMED framework, a form of load balancing can be implemented on selected strategy profiles for a subset of the destination networks whose traffic routing can be coordinated. We consistently integrate IGP weight optimization operations and peering link congestion controls, which increases the number of possible Nash equilibria and, thus, the importance of coordination schemes to select the most efficient ones. Sect. IV presents practical implementation aspects. Sect. V reports the results from realistic simulations and comments the significant gains the ClubMED framework can offer with respect to the current practice. Finally, Sect. VI summarizes the paper. II. RATIONALES A. BGP, route deflection and congestion It is worth briefly reminding how the inter-AS route se- lection is performed via BGP. When multiple AS paths to a destination network prefix are available, a cascade of criteria is employed to compare them. The first is the “local preference” through which local policies, mainly guided by economic issues, can be applied: e.g., a peering link (i.e., free transit) is preferred to a transit link (transit fees). Marking routes with local preferences, an AS can thus implement peering and transit settlements. The subsequent BGP criteria incorporate purely operational network issues: smaller AS hop count, smaller MED, closer egress point (also called “hot-potato”), more recent route. If not enough, the AS path learned by the router with the smaller IP is selected (rule also called “tie- breaking”). Considering these criteria, BGP selects the best AS path which is the single one advertised to the neighbours (if not filtered by local policies). 978-1-4244-424 - /09/$25.00 (c)2009 IEEE 54