A Lesson in BGP Visibility

August 5, 2008 at 16:20 · Filed under Measurement, Routers & Routing

While Olaf and I were looking for other things, we stumbled on a revealing sub-experimental result.

  • We announced a /25 prefix via BGP from our research routers at the Westin in Seattle
  • Sprint did not listen to it
  • Verio/NTT did, and said they propagated to their customers but not their peers
  • We looked at BGP feeds from RouteViews, RIS, and 700+ other BGP feeds
  • BGP data said the /25 reached 15 ASs
  • From a prefix in the source /25, we probed IP addresses in over 20,000 ASs
  • 1023 ASs replied
  • I.e. RV et alia showed a shockingly small fraction of the real AS topology, less than 1.5%

Interestingly, the AS path length shown in the 15 ASs visible in BGP was 3, while pingability and the BGP path length for a /20 was the normal >4. See the diagram.

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