Impact of prefix-match changes on IP reachability

  • Authors:
  • Yaping Zhu;Jennifer Rexford;Subhabrata Sen;Aman Shaikh

  • Affiliations:
  • Princeton University, Princeton, NJ, USA;Princeton University, Princeton, NJ, USA;AT&T Labs-Research, Florham Park, NJ, USA;AT&T Labs-Research, Florham Park, NJ, USA

  • Venue:
  • Proceedings of the 9th ACM SIGCOMM conference on Internet measurement conference
  • Year:
  • 2009

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Abstract

Although most studies of Internet routing treat each IP address block (or prefix) independently, the relationship between prefixes is important because routers ultimately forward packets based on the "longest-matching prefix." In fact, the most-specific prefix for a given destination address may change over time, as BGP routes are announced and withdrawn. Even if the most-specific route is withdrawn, routers may still be able to deliver packets to the destination using a less-specific route. In this paper, we analyze BGP update messages and Netflow traffic traces from a large ISP to characterize both the changes to the longest-matching prefix over time and the resulting effects on end-to-end reachability of the destination hosts. To drive our analysis, we design and implement an efficient online algorithm for tracking changes in the longest-matching prefix for each IP address. We analyze the BGP message traces to identify the reasons for prefix-match changes, including failures, route flapping, sub-prefix hijacking, and load-balancing policies. Our preliminary analysis of the Netflow data suggests that the relationship between BGP updates and IP reachability is sometimes counterintuitive.