Humpty Dumpty: Putting iBGP Back Together Again

Humpty Dumpty is the anthropomorphic nursery-rhyme egg broken into many pieces. Similarly, we have many pieces of measurement data to represent the current iBGP state. However, unlike the nursery-rhyme where the King's men couldn't put Humpty together again, we present a systematic approach to putting all the pieces of measured iBGP data together to obtain a more complete picture of a network's routing state. Our technique determines the decisions made by all routers in a network. It is efficient, has no assumptions about router configuration and is accurate. We present a case-study of a large Tier-2 ISP, finding for those routers with adequate measurement infrastructure, we consistently find the egress location for 99.9999% of (router , prefix ) pairs. Further, for the 85% of routers without measurement infrastructure we predict their decisions. This technique has been successfully applied in a `what-if' scenario and has future applications in the real-time analysis of routing decisions.