Where the Sidewalk Ends Extending the Internet AS Graph Using Traceroutes from P2P Users

1. Where the Sidewalk EndsExtending the Internet AS Graph Using Traceroutes from P2P Users Kai Chen, Dave Choffnes, Rahul Potharaju, Yan Chen, Fabián Bustamante, Dan Pei*, Yao Zhao EECS Dept, Northwestern University AT&T Labs - Research* 1 K. Chen et al, where the Sidewalk Ends

2. Internet and AS topology AS topology graph is important Routing protocol design, performance evaluation, Internet security … Currently, the publicly available AS graph is incomplete ISPs do not want to disclose their connectivity 2 K. Chen et al, Where the Sidewalk Ends

3. Existing approaches Passive measurement BGP routing tables/updates Active measurement Traceroutes Limitation Small # of VPs (ASes with monitors inside) In most cases, one/two monitors in each VP 3 K. Chen et al, Where the Sidewalk Ends

4. Motivation A promising platform should: have many more VPs allow active measurement scale with the growing Internet P2P is a natural fit ! 4 K. Chen et al, Where the Sidewalk Ends

5. Our approach Increase the # of VPs using P2P users Ono, an plugin to Vuze Bitorrent client, installed by 800K users in 7310 distinct ASes Active traceroutes from edge of the Internet Map IP paths to AS paths, extract AS links 5 K. Chen et al, Where the Sidewalk Ends

6. Roadmap Background Motivation Methodology, Dataset and Validation The newly-identified AS links Root causes Conclusion K. Chen et al, Where the Sidewalk Ends

7. From IP path to AS path IP path adjustment 1. Process incomplete AS paths 2. Correct false AS links Raw IP level traceroutes Publicly Mapped AS paths Final AS paths and AS links K. Chen et al, Where the Sidewalk Ends

8. IP path adjustment • Problematic traceroute IP paths • unresponsive IP hops • repeated IP hops • IP loops • Solutions • trim unresponsive (*) hops at the end • remove rest problematic traceroute paths K. Chen et al, Where the Sidewalk Ends

9. Process incomplete AS paths • Incomplete AS paths • unmapped hop within an AS • unmapped hop between ASes • Multiple Origin AS at the end • Solutions [Mao et al Sigcomm’03] • map that hop to the same AS • try match that hop to neighboring AS using DNS/Whois • assume multi-homing without BGP K. Chen et al, Where the Sidewalk Ends

10. Correct false traceroute AS links • Reasons for false links • private peering • Internet eXchange points (IXPs) • sibling ASes • unannounced IP addresses • using outgoing interface for ICMP • Solution • Use BGP AS paths to correct possibly false traceroute AS links K. Chen et al, Where the Sidewalk Ends

11. How to correct false AS links • Key observation [Mao et al, Sigcomm03] • Discrepancies: one extra/missing/substitute hop • Basic idea • Compare traceroute AS path with BGP paths, for every new link: could it be false? • If possibility found, then correct the possibly false AS links • Could filter out true links together with false links K. Chen et al, Where the Sidewalk Ends

12. Example heuristics: missing hop [… A B C D …] is a traceroute AS path and AS link B-C is new. See [… B X C …] in BGP AS path Link B-C could be false due to: 1. private peering 2. sibling ASes 3. using outgoing interface for ICMP query 4. unannounced IP addresses 12 K. Chen et al, Where the Sidewalk Ends

13. Example heuristics: substitute hop [… A B C D …] is a traceroute AS path and AS link B-C is new. See [… A X C …] (or [… B X D …]) in BGP AS path Link B-C could be false due to: 1. unannounced IP addresses 2. sibling ASes 3. using outgoing interface for ICMP query 13 K. Chen et al, Where the Sidewalk Ends

14. Example heuristics: extra hop [… A B C D …] is a traceroute AS path and AS link B-C is new. See [… A C …] (or [… B D …]) in BGP AS path Link B-C could be false due to: 1. IXPs or sibling ASes 2. unannounced IP addresses 3. using outgoing interface for ICMP query 14 K. Chen et al, Where the Sidewalk Ends

15. Dataset and Validation Traceroute data from Ono (12/2007 – 9/2008) From Ono hosts to any connected BT peer 541 million IP paths from end hosts Public BGP data (12/2007 – 9/2008) Routeviews/RIPE, etc Data from UCLA-IRL, contains IRR, route severs, looking glasses (thanks for their work!) Ground-truth data of a Tier-1 AS (for validation) All 48% false links with this tier-1 AS are filtered out! 15 K. Chen et al, Where the Sidewalk Ends

16. Newly-identified AS links • 12.86% more customer-provider (C-P) AS links • 40.99% more peering (P-P) links • Very few tier-1 AS links found (0~3%) Relationship [Gao 04] Tiers [Oliveira 08] 16 K. Chen et al, Where the Sidewalk Ends

17. Patterns of new links 17 K. Chen et al, Where the Sidewalk Ends

18. Observations • VP can miss AS links of itself (a) and its upstream providers (b) • Missing peering links can be on the higher layers than VPs , such as (b) K. Chen et al, Where the Sidewalk Ends

19. Observations • VP can miss AS links of itself (a) and its upstream providers (b) • Missing peering links can be on the higher layers than VPs , such as (b) K. Chen et al, Where the Sidewalk Ends

20. Root causes of missing links • Route aggregation • Routing table reduction, VP cannot see the links behind aggregation • Sub-optimal path to VP • Path-vector routing protocol, choose the best path for routing, VP cannot see links on sub-optimal ones • Valley-free routing policy • Policy-driven, an AS won’t export routes from peers or providers to another peers or provider

21. Observations Missing links can have multiple reasons 75.02% missing links can be related to the three reasons simultaneously Route aggregation is a dominant factor 76.10% missing links are related to this 98% of the missing links are related to BGP policies (sub-optimal + valley-free) 21 K. Chen et al, where the sidewalk ends

22. Caveats Validation with one tier-1 AS does not imply correctness with all Inferred relationships can be wrong Affects classification and root causes 22 K. Chen et al, where the sidewalk ends

23. Summary P2P systems provide a platform for significantly increasing VPs to do AS topology measurement Develop a series of heuristics to infer the AS links from our P2P traceroutes A more complete AS map than what's available Our identified links are available: http://aqualab.cs.northwestern.edu/projects/SidewalkEnds.html Your feedback is welcome. 23 K. Chen et al, where the sidewalk ends

24. Q & A? Thanks. 24 K. Chen et al, where the sidewalk ends