Stable Route Selection for Interdomain Traffic Engineering

2005

We present a general model of interdomain route selection to study interdomain traffic engineering. In this model, the routing of multiple destinations can be coordinated. Thus the model can capture general traffic engineering behaviors such as load balancing and link capacity constraints. We first identify potential routing instability and inefficiency of interdomain traffic engineering. We then derive a sufficient condition to guarantee convergence. We also show that the constraints on local policies imposed by business considerations in the Internet can guarantee stability without global coordination. Using realistic Internet topology, we evaluate the extent to which routing instability of interdomain traffic engineering can happen when the constraints are violated

IEEE Network, 2005

In this paper, we investigate a model of route selection for interdomain traffic engineering where the routing to multiple destinations can be coordinated. We identify potential routing instability and inefficiency problems, and derive a set of practical guidelines to guarantee stability without global coordination. Using a realistic Internet topology, we show that route oscillations can happen even when a small number of ASes coordinate route selection for just a small number of destinations, if the coordination does not follow our guidelines. We further extend our model so that 1) ASes can adopt any route selection algorithms in a class of algorithms which we call rational route selection algorithms; and 2) the local ranking of routes of an AS can depend on ingress traffic patterns. We show that persistent route oscillations can happen in certain network settings even if the ASes strictly follow the constraints imposed by business considerations, and adopt any rational route selection algorithms. for valuable comments. We are also grateful to the anonymous reviewers and the shepherd Olivier Bonaventure for their valuable comments. 1 there is no AS whose routing policies require it to coordinate its route selection among multiple destinations. On the other hand, a fundamental feature of route selection for interdomain traffic engineering in particular and traffic engineering in general is that route selection constraints (e.g., traffic assigned to a link remains within link capacity) and/or objectives (e.g., balancing the load) involve the route selection of multiple destinations. Thus, in route selection for interdomain traffic engineering, whether a route will be chosen for a given destination will depend on what routes are available or chosen for other destinations. For example, if an AS selects routes for each destination independently without considering the chosen/available routes of other destinations, in the worst case it may choose the same access link for all destinations, violating link capacity constraints and/or causing load imbalance. Second, the previous studies focus on the stability of a homogeneous network where each AS runs the same specific interdomain route selection algorithm (i.e., the BGP-based greedy route selection algorithm). However, with increasing usage of route selection for interdomain traffic engineering, route selection algorithms with more sophisticated strategies are likely to be designed and deployed in the Internet. Thus it is necessary to analyze the stability of a heterogeneous network where ASes may adopt a larger class of route selection algorithms beyond the greedy strategy. Third, the previous studies focus on local policies which rank only the egress routes; that is, they assume that the local ranking of egress routes at each AS is independent of the inbound traffic pattern of that AS. However, in practice, the local policies of ASes may involve both the egress routes and the pattern of inbound traffic. In the last few years, several traffic-demand-matrix-based traffic engineering algorithms have been proposed. Although such route selection algorithms have been shown to be effective, the evaluations often assume that the route selection of each AS does not affect the inbound traffic, whereas the inbound traffic is likely to change with the chosen egress routes, introducing unexpected interactions. Thus it is necessary to analyze the stability of route selection algorithms implementing local policies that take into account inbound traffic patterns.

European Transactions on Telecommunications

We study the interdomain traffic as seen by a non-transit ISP, based on a six days trace covering all the interdomain links of this ISP. Our analysis considers the relationships between the interdomain traffic and the interdomain topology. We first discuss the day-today stability of the interdomain traffic matrix to evaluate the feasibility of interdomain traffic engineering. Then, we study the variability of the interdomain flows for several aggregation levels (prefix, AS and sink tree) and with respect to the interdomain topology seen by BGP. We show that despite the important variability of interdomain flows, it would be useful for a non-transit ISP to traffic engineer its access traffic by relying on a sink tree aggregation level.

13TH IEEE International Conference on Network Protocols (ICNP'05), 2005

The recent discovery of instability caused by the interaction of local routing policies of multiple ASes has led to extensive research on the subject. However, previous studies analyze stability under a specific route selection algorithm. In this paper, instead of studying a specific route selection algorithm, we study a general class of route selection algorithms which we call rational route selection algorithms. We present a sufficient condition to guarantee routing convergence in a heterogeneous network where each AS runs any rational route selection algorithm. Applying our general results, we study the potential instability of a network where the preference of an AS depends on not only its egress routes to the destinations but also its inbound traffic patterns (i.e., the distribution of incoming traffic from its neighbors). We show that there exist networks which will have persistent route oscillations even when the ASes strictly follow the constraints imposed by business considerations, and adopt any rational route selection algorithms.

2004

We study the interdomain traffic as seen by a non-transit ISP, based on a six days trace covering all the interdomain links of this ISP. Our analysis considers the relationships between the interdomain traffic and the interdomain topology. We first discuss the day-to-day stability of the interdomain traffic matrix to evaluate the feasibility of interdomain traffic engineering. Then, we study the variability of the interdomain flows for several aggregation levels (prefix, AS and sink tree) and with respect to the interdomain topology seen by BGP. We show that despite the important variability of interdomain flows, it would be useful for a non-transit ISP to traffic engineer its access traffic by relying on a sink tree aggregation level.

2009

The Border Gateway Protocol (BGP) handles the task of establishing routes between the Autonomous Systems (ASes) that make up the Internet. It is known that it is possible for a group of ASes to define local BGP policies that lead to global BGP protocol oscillations. We close a long standing open question by showing that, for any network, if two stable routing outcomes exist then persistent BGP route oscillations are possible. This is the first non-trivial necessary condition for BGP safety. It shows that BGP safety must always come at the price of severe restrictions on ASes' expressiveness in their choice of routing policies. The technical tools used in our proof may be helpful in the detection of potential route oscillations and their debugging.

Computer Communication Review, 2003

Network operators must have control over the flow of traffic into, out of, and across their networks. However, the Border Gateway Protocol (BGP) does not facilitate common traffic engineering tasks, such as balancing load across multiple links to a neighboring AS or directing traffic to a different neighbor. Solving these problems is difficult because the number of possible changes to routing policies is too large to exhaustively test all possibilities, some changes in routing policy can have an unpredictable effect on the flow of traffic, and the BGP decision process implemented by router vendors limits an operator's control over path selection.

Sigmetrics Performance Evaluation Review, 2000

The Border Gateway Protocol (BGP) allows an autonomous system (AS) to apply diverse local policies for selecting routes and propagating reachability information to other domains. However, BGP permits ASes to have conflicting policies that can lead to routing instability. This paper proposes a set of guidelines for an AS to follow in setting its routing policies, without requiring coordination with other ASes. Our approach exploits the Internet's hierarchical structure and the commercial relationships between ASes to impose a partial order on the set of routes to each destination. The guidelines conform to conventional traffic-engineering practices of ISPs, and provide each AS with significant flexibility in selecting its local policies. Furthermore, the guidelines ensure route convergence even under changes in the topology and routing policies. Drawing on a formal model of BGP, we prove that following our proposed policy guidelines guarantees route convergence. We also describe how our methodology can be applied to new types of relationships between ASes, how to verify the hierarchical AS relationships, and how to realize our policy guidelines. Our approach has significant practical value since it preserves the ability of each AS to apply complex local policies without divulging its BGP configurations to others.

2004

In this paper we study the behavior of Internet traffic on the ASlevel topology and discuss its implications on interdomain traffic engineering. We rely on two notable interdomain traffic traces, the first is one month long and the other is one day long. This study shows that interdomain paths are stable for a large majority of the traffic from a routing viewpoint. We show that the aggregation of the traffic occurring on the AS-level graph is essentially limited to direct peers, with almost no aggregation occurring at larger AS hop distances. Furthermore, only part of the AS paths of the AS-level topology that see a lot of traffic are stable, when considering their presence among the largest AS paths on a hourly basis. Relying on the largest AS paths in traffic over a time window to capture the traffic over the next time interval discloses the important variability of the traffic seen by the largest AS paths in traffic. Interdomain traffic engineering is hence due to be difficult because of the limited traffic aggregation on the AS-level topology and the important topological variability of the traffic for a significant percentage of the total traffic.

Abstract���Multihoming in combination with route optimization tools working in short timescales is becoming a common practice in order to improve end-to-end QoS at the edge of the Internet. Nevertheless, the stability repercussions of these selfish practices under massive utilization are absolutely unpredictable.