The Border Gateway Protocol (BGP) is used today by routers of all Autonomous Systems (AS) in the Internet. BGP is responsible for end-to-end reachability in the Internet. BGP routers have to exchange routes towards about 200,000 prefixes (blocks of IP addresses). Inside each AS, routers are using internal iBGP sessions to exchange their best route with other routers. The objective of an iBGP topology is to redistribute BGP routes inside the whole AS. In large ASs, some BGP routers are used as route reflectors because it reduces the total number of sessions needed for this route redistribution. Checking the correctness of iBGP configuration [1] and detecting potential problems inside the iBGP [2] are particularly difficult when route reflection [3] is used. The scalability of route reflection compared to an iBGP full-mesh comes at the cost of opacity in the choice of the best routes by the routers inside the AS. This opacity induces problems like suboptimal route choices in the IGP cost, deflection and forwarding loops. We propose to check for the optimality of the routes choice in a route reflection graph. We do so without requiring to simulate the complex operations of the BGP protocol. Our check procedure is applied to a tier-1 AS. Our simulations show that a significant fraction of suboptimal path choices may occur, between 10 and 30% in realistic cases.
Abstract. The Border Gateway Protocol (BGP) is used today by all Autonomous Systems (AS) in the Internet. Inside each AS, iBGP sessions distribute the external routes among the routers. In large ASs, relying on a full-mesh of iBGP sessions between routers is not scalable, so route-reflection is commonly used. The scalability of route-reflection compared to an iBGP full-mesh comes at the cost of opacity in the choice of best routes by the routers inside the AS. This opacity induces problems like suboptimal route choices in terms of IGP cost, deflection and forwarding loops. In this work we propose a solution to design iBGP routereflection topologies which lead to the same routing as with an iBGP full-mesh and having a minimal number of iBGP sessions. Moreover we compute a robust topology even if a single node or link failure occurs. We apply our methodology on the network of a tier-1 ISP. Twice as many iBGP sessions are required to ensure robustness to single IGP failure. The number of required iBGP sessions in our robust topology is however not much larger than in the current iBGP topology used in the tier-1 ISP network.
This paper studies how intradomain routing instability relates to events in network trouble tickets for two networks: a VPN provider and the Internet2 backbone network. Our goal in performing this joint analysis of routing and trouble tickets is to better understand the likely underlying causes of intradomain routing instability. We develop a method to correlate trouble tickets with instability events and find that, although unplanned events last longer than scheduled maintenance, there is no single underlying cause for most instability, and that these causes differ across networks. In comparison to a similar study from Labovitz et al. from ten years ago, we find that, while certain causes of instability such as maintenance and circuit problems remain significant, power issues have become much less prevalent, and software-related problems have become more common.
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