Abha Ahuja

Delayed Internet routing convergence

This paper examines the latency in Internet path failure, failover, and repair due to the convergence properties of interdomain routing. Unlike circuit-switched paths which exhibit failover on the order of milliseconds, our experimental measurements show that interdomain routers in the packet-switched Internet may take tens of minutes to reach a consistent view of the network topology after a fault. These delays stem temporary routing table fluctuations formed during the operation of the Border Gateway Protocol (BGP) path selection process on Internet backbone routers. During these periods delayed convergence, we show that end-to-end Internet paths will experience intermittent loss of connectivity, as well as increased packet loss and latency. We present a two-year study of Internet routing convergence through the experimental instrumentation of key portions of the Internet infrastructure, including both passive data collection and fault-injection machines at Internet exchange points. Based on data from the injection and measurement of several hundred thousand interdomain routing faults, we describe several unexpected properties of convergence and show that the measured upperbound on Internet interdomain routing convergence delay is an order of magnitude slower than previously thought. Our analysis also shows that the upper theoretic computational bound on the number of router states and control messages exchanged during the process of BGP convergence is factorial with respect to the number of autonomous systems in the Internet. Finally, we demonstrate that much of the observed convergence delay stems form specific router vendor implementation decisions and ambiguity in the BGP specification.

Experimental study of Internet stability and backbone failures

In this paper, we describe an experimental study of Internet topological stability and the origins of failure in Internet protocol backbones. The stability of end-to-end Internet paths is dependent both on the underlying telecommunication switching system, as well as the higher level software and hardware components specific to the Internets packet-switched forwarding and routing architecture. Although a number of earlier studies have examined failures in the public telecommunication system, little attention has been given to the characterization of Internet stability. We provide analysis of the stability of major paths between Internet Service Providers based on the experimental instrumentation of key portions of the Internet infrastructure. We describe unexpectedly high levels of path fluctuation and an aggregate low mean time between failures for individual Internet paths. We also provide a case study of the network failures observed in a large regional Internet backbone. We characterize the type, origin, frequency and duration of these failures.