Existing multicast routing mechanisms were intended for use within regions where a group is widely represented or bandwidth is universally plentiful. When group members, and senders to those group members, are distributed sparsely across a wide area, these schemes are not efficient; data packets or membership report information are occasionally sent over many links that do not lead to receivers or senders, respectively. Wehave developed a multicast routing architecture that efficiently establishes distribution trees across wide area internets, where many groups will be sparsely represented. Efficiency is measured in terms of the state, control message processing, and data packet processing, required across the entire network in order to deliver data packets to the members of the group. Our Protocol Independent Multicast (PIM) architecture: (a) maintains the traditional IP multicast service model of receiver-initiated membership; (b) can be configured to adapt to different multicast group and network characteristics; (c) is not dependent on a specific unicast routing protocol; and (d) uses soft-state mechanisms to adapt to underlying network conditions and group dynamics. The robustness, flexibility, and scaling properties of this architecture make it well suited to large heterogeneous inter-networks.

The Border Gateway Protocol (BGP) is the de facto interdomain routing protocol used to exchange reachability information between Autonomous Systems in the global Internet. BGP is a path-vector protocol that allows each Autonomous System to override distance-based metrics with policy-based metrics when choosing best routes. Varadhan et al. [18] have shown that it is possible for a group of Autonomous Systems to independently define BGP policies that together lead to BGP protocol oscillations that never converge on a stable routing. One approach to addressing this problem is based on static analysis of routing policies to determine if they are safe. We explore the worst-case complexity for convergenceoriented static analysis of BGP routing policies. We present an abstract model of BGP and use it to define several global sanity conditions on routing policies that are related to BGP convergence/divergence. For each condition we show that the complexity of statically checking it is either N...

Abstract—Dynamic routing protocols such as RIP and OSPF essentially implement distributed algorithms for solving the shortest paths problem. The border gateway protocol (BGP) is currently the only interdomain routing protocol deployed in the Internet. BGP does not solve a shortest paths problem since any interdomain protocol is required to allow policy-based metrics to override distance-based metrics and enable autonomous systems to independently define their routing policies with little or no global coordination. It is then natural to ask if BGP can be viewed as a distributed algorithm for solving some fundamental problem. We introduce the stable paths problem and show that BGP can be viewed as a distributed algorithm for solving this problem. Unlike a shortest path tree, such a solution does not represent a global optimum, but rather an equilibrium point in which each node is assigned its local optimum. We study the stable paths problem using a derived structure called a dispute wheel, representing conflicting routing policies at various nodes. We show that if no dispute wheel can be constructed, then there exists a unique solution for the stable paths problem. We define the simple path vector protocol (SPVP), a distributed algorithm for solving the stable paths problem. SPVP is intended to capture the dynamic behavior of BGP at an abstract level. If SPVP converges, then the resulting state corresponds to a stable paths solution. If there is no solution, then SPVP always diverges. In fact, SPVP can even diverge when a solution exists. We show that SPVP will converge to the unique solution of an instance of the stable paths problem if no dispute wheel exists. Index Terms—BGP, Border Gateway Protocol, interdomain routing, internet routing, path vector protocols, stable routing.

Route flap damping is considered to be a widely deployed mechanism in core routers that limits the widespread propagation of unstable BGP routing information. Originally designed to suppress route changes caused by link flaps, flap damping attempts to distinguish persistently unstable routes from routes that occasionally fail. It is considered to be a major contributor to the stability of the Internet routing system.

IP routing requires the cooperation of a large number of Autonomous Systems (ASes) via the Border Gateway Protocol (BGP). Each AS applies local policies for selecting routes and propagating routes to others, with important implications for the reliability and stability of the global system. In and of itself, BGP does not ensure that every pair of hosts can communicate. In addition, routing policies are not guaranteed be safe, and may cause persistent protocol oscillations. Backup routing is often used to increase the reliability of the network under link and router failures, at the possible expense of safety. This paper presents two models for backup routing that increase global network reliability without compromising safety. Indeed, our models are inherently safe in the sense that they remain safe under any combination of link and router failures. I.

The Border Gateway Protocol (BGP) is the routing protocol used to maintain connectivity between autonomous systems in the Internet. Empirical measurements have shown that there can be considerable delay in BGP convergence after routing changes. One contributing factor in this delay is a BGP-specific timer used to limit the rate at which routing messages are transmitted. We use the SSFNet simulator to explore the relationship between convergence time and the configuration of this timer. For each simple network topology simulated, we observe that there is an optimal value for the rate-limiting timer that minimizes convergence time. 1

An IP routing protocol is safe if it is guaranteed to converge in the absence of network topology changes. BGP, currently the only interdomain routing protocol employed on the Internet, is not safe in this sense. It may seem that the source of BGP's potential divergence is inherent in the requirements for any interdomain routing protocol --- policy-based metrics must be allowed to override distance-based metrics, and each autonomous system must be allowed to independently define its routing policies with little or no global coordination. In this paper we present a Simple Path Vector Protocol (SPVP) that captures the underlying semantics of BGP by abstracting away all nonessential details. We then add a dynamically computed attribute to SPVP routing messages, called the route history. Protocol oscillations caused by policy conflicts produce routes whose histories contain cycles. These cycles identify the policy conflicts and the autonomous systems involved. SPVP is made safe by automati...

The Border Gateway Protocol, BGP, is currently the only interdomain routing protocol employed on the Internet. As required of any interdomain protocol, BGP allows policy-based metrics to override distance-based metrics and enables each autonomous system to independently define its routing policies with little or no global coordination. Varadhan et al. [11] have shown that there are collections of routing policies that together are not safe in the sense that they can cause BGP to diverge. That is, an unsafe collection of routing policies can result in some autonomous systems exchanging BGP routing messages indefinitely, without ever converging to a set of stable routes. In this paper we present sufficient conditions on routing policies that guarantee BGP safety. We use a new formalism, called the Simple Path Vector Protocol (SPVP), that is designed to capture the underlying semantics of any path vector protocol such as BGP. We identify a certain circular set of relationships between rou...

Mapping the Internet is a major challenge for network researchers. It is the key to building a successful modeling tool able to generate realistic graphs for use in networking simulations. In this paper we provide a detailed analysis of the inter-domain topology of the Internet. The collected data and the resulting analysis began in November 1997 and cover a period of two and a half years. We give results concerning major topology properties (nodes and edges number, average degree and distance, routing policy, etc.) and main distributions (degree, distance, etc.). We also present many results about the trees of this network. The evolution of these properties is reviewed and major trends are highlighted. We propose some empirical laws that match this current evolution. Four new power-laws concerning the number of shortest paths between node pairs and the tree size distribution are provided with their detailed validation.

(URI) program administered by the Office of Naval Research (ONR). A shortened form of this work has