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Geographic Locality of IP Prefixes

Geographic Locality of IP Prefixes. Mythili Vutukuru Joint work with Michael J. Freedman, Nick Feamster and Hari Balakrishnan Internet Measurement Conference ‘05. Autonomous Systems (ASes) IP Prefixes in BGP messages “Routing handles”

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Geographic Locality of IP Prefixes

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  1. Geographic Locality of IP Prefixes Mythili Vutukuru Joint work with Michael J. Freedman, Nick Feamster and Hari Balakrishnan Internet Measurement Conference ‘05

  2. Autonomous Systems (ASes) IP Prefixes in BGP messages “Routing handles” Granularity of routing handle – tradeoff between routing table size and ability to control traffic Is prefix the right granularity? C B A Motivation 10.0.0.0/16

  3. 10.1/16 10.3/16 10.5/16 10.1.0.0/16 10.3.0.0/16 10.5.0.0/16 Too fine-grained? X X B X A X • Discontiguous prefixes from same location • Likely to share fate • Multiple routing table entries to be updates • Close in geography, far in IP space →fine-grained

  4. Too coarse-grained? 10.0/16 10.0/16 10.0/15 C B A 10.1/16 10.0/15 10.1/16 B does not aggregate B aggregates • Contiguous prefixes from different locations • Aggregate → less control over traffic • Artificially inflates “opportunities” for aggregation • Close in IP space, far geographically → coarse-grained

  5. Questions we investigate IP space Geography Granularity Far Close Fine-grained Close Far Coarse-grained How often do ASes announce discontiguous prefixes from same location? How often do ASes announce contiguous prefixes from different locations? Correlation - locality in IP space & geographic locality

  6. Major Findings • Discontiguous prefixes, close geographically • 70% of discontiguous prefix pairs • Fragmented allocation to fate-sharing entities • Contiguous prefixes, far geographically • 25% of contiguous prefix pairs • Unsuitable to express traffic control policy

  7. Uses naming conventions of routers – city names embedded in DNS names Method GOAL: Associate an IP prefix with a set of locations (cities) X X Location(city) CoralCDN[1] Web clients Content servers DNS names undns[2] IPs IP Prefix Random IPs Routeviews[3] Traceroute [1] http://www.coralcdn.org [2] http://www.scriptroute.org [3] http://www.routeviews.org

  8. Prefixes too fine-grained 70% of discontiguous prefixes have same location 65% due to fragmented allocation • Analyzed top 20 <AS, location> pairs • 23% of them allocated on the same day

  9. 10.1/16 10.3/16 10.5/16 Implications • Renumber? • Change granularity of routing?? • Eg: PoP level <A,location> <A,location> B A 10.1.0.0/16 10.3.0.0/16 10.5.0.0/16

  10. Prefix AS Path Prefix AS Path Location Prefixes too coarse grained • 25% of contiguous prefixes - different location • CIDR Report[4] • Same AS path + close geographically 64% reduction 10.0/16 A B C D 10.0/15 A B C D 10.1/16 A B C D 20% reduction 10.0/15 A B C D L1 10.1/16 A B C D L1 10.0/16 A B C D L1 [4] http://www.cidr-report.org

  11. Implications • Potential for aggregation over-stated • Aggregate too coarse grained – poor traffic control

  12. Take-home lessons • Is prefix the right granularity for routing? • Prefix too fine-grained • Discontiguous prefixes from same location • Causes many routing table updates • Change routing granularity: group by shared fate? • Prefix too coarse-grained • Contiguous prefixes from different locations • Potential for aggregation is overstated • Aggregate prefix unfit for traffic control Questions?

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