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Inferring AS Relationships

Inferring AS Relationships. The Problem. One view AS relationships  BGP route tables The other view BGP route tables  AS relationships Available Internet route logs Oregon Routeviews project European RIPE project. Why Inference?. Connectivity does not imply reachability

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Inferring AS Relationships

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  1. Inferring AS Relationships

  2. The Problem • One view • AS relationships  BGP route tables • The other view • BGP route tables  AS relationships • Available Internet route logs • Oregon Routeviews project • European RIPE project

  3. Why Inference? • Connectivity does not imply reachability • End-to-end performance cannot be inferred from AS (connectivity) graph • Contractual agreements between ISPs are proprietary ISP B ISP A customer ISP C

  4. Annotated AS Graph Provider-to-customer Peer-to-peer Sibling-to-sibling

  5. Selective Export Rule • Consider AS u and AS v  provider(u)  peer(u) • For each best route r of u, if r is a provider / peer route of u, then export(v,u)[{r}] = {} • Consider AS u and AS v  customer(u)  sibling(u) • There is a best route r of u s.t. r is a provider / peer route of u, and export(v,u)[{r}]  {}

  6. Transit Implications • ASes u and v are peers iff neither u transits traffic for v nor v transits traffic for u • AS u is provider of v iff u transits traffic for v and v does not transit traffic for u • ASes u and v have a sibling relationship iff both u transits traffic for v and v transits traffic for u

  7. Routing Table Entry Information • If u0’s BGP table contains route e, where e.as_path = (u1, …, un), then • ui selects route with as_path (ui+1, … un) as best route to prefix • ui exports its best route to ui-1

  8. Valley-free Property • AS path of BGP routing table entry has following valley-free property • A provider-customer edge can be followed by only provider-customer or sibling-sibling edges • A peer-peer edge can be followed only by provider-customer or sibling-sibling edges

  9. Example Paths 6 2 3 1 4 5 Valley-free: (1,2,3) (1,2,6,3) Non valley-free: (1,4,3) (1,4,5,3)

  10. More Routing Entry Patterns • Downhill path: a sequence of edges that are either provider-customer or sibling-sibling • Maximal downhill path: longest such path • Uphill path: a sequence of edges that are either customer-provider or sibling-sibling • Maximal uphill path: longest such path

  11. BGP Path Patterns • An uphill path • A downhill path • An uphill path followed by a downhill path • An uphill path followed by a peer-peer edge • A peer-peer edge followed by a downhill path • An uphill path followed by a peer-peer edge, which is followed by a downhill path

  12. Heuristic Inference Alogrithm • Provider typically has a larger size than its customer • Size of AS is typically proportional to its degree in AS graph • The uphill (downhill) top provider of an AS path should be the AS with highest degree among all ASes in its maximal uphill (downhill) path • Top provider is the AS with higher degree between the uphill and downhill top providers

  13. Inference Algorithm (cont’d) • Consecutive AS pairs that appear before the top provider in the AS path are customer-provider or sibling-sibling edges • Consecutive pairs that appear after the top provider in the AS path are provider-customer or sibling-sibling edges • Pairs of top provider and top provider’s neighbor are the peer-peer edges

  14. Provider-customer and Sibling Relationships • Given AS path, find top provider • Consecutive AS pairs before top provider are customer-provier or sibling-sibling edges • If (u1,u2) appears, then u2 provides transit for u1 • Consecutive pairs after top provider are provider-customer or sibling-sibling • If (u1,u2) appears, then u1 provides transit for u2 • u1 is provider of u2 iff u1 provides transit for u2 but u2 does not provide transit for u1 • AS pair have sibling relationship if they provide transit for each other

  15. Basic Algorithm • Given BGP routing tables, run in three phases • Phase 1: compute the degree for each AS • Phase 2: parse AS path to initialize consecutive AS pair’s transit relationship • Phase 3: assign relationships to AS pairs based on transit results

  16. Refined Algorithm • Basic algorithm may misclassify if some BGP speakers are misconfigured • E.g., configured to provide transit between two providers • Assume that the fraction of misconfigured BGP speakers is small • Count the number of routing table entries that infer a transit relationship • Confirm transit only of number exceeds threshold L

  17. Peering Relationships • At most one peer-to-peer link on each path • Top provider either peers with its left neighbor or right neigbor in the path • Three phases • Phase 1: classify the provider-customer and sibling relationships • Phase 2: identify AS pairs that may have a peering relationship • Neighbor of top provider in an AS path, not a sibling of the provider, and has higher degree than the other neighbor if neither neighbor of the top provider is a sibling • Phase 3: confirm candidate AS pairs by checking for “similar” degrees of the two ASes in a pair

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