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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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Presentation Transcript

The problem
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
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


Annotated as graph
Annotated AS Graph

Provider-to-customer

Peer-to-peer

Sibling-to-sibling


Selective export rule
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}]  {}


Transit implications
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


Routing table entry information
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


Valley free property
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


Example paths
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)


More routing entry patterns
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


Bgp path patterns
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


Heuristic inference alogrithm
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


Inference algorithm cont d
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


Provider customer and sibling relationships
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


Basic algorithm
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


Refined algorithm
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


Peering relationships
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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