Inferring Autonomous System Relationships in the Internet Lixin Gao

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Inferring Autonomous System Relationships in the
InternetLixin Gao
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• Background
• Network is typically modelled as a graph.
• Does it work in BGP?
• Routing in BGP is controlled by the policy. Does
  connectivity imply reachability?
• Need to have AS relation to characterize the
  Internet.
• BGP allows each AS to choose its own policy in
  selecting routes and propagating reachability
  information.
• The policies are constrained only by the
  contractual commercial agreements.
• What are the types of the AS relationship?
• What kind of paths appear in the BGP routing
  table?
• Is it possible to infer the AS relationship from
  public information (BGP routing table)

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• Network model
• connectivity between ASes can be modeled using an
  AS graph, G (V, E).
• Import policies transform incoming routes.
• u sends v a set of routes R, import (u, v)R
  represents the set of updated routes after the
  import policies are applied.
• E.g. if v in r.as_path then import (u, v)r
  
• The best path to d, B(u, d) is selected from the
  updated routes from all neighbor.
• Export policies export(v, u) is applied to the
  best routes before they are send to neighbor v
• Routing table enable is either B(u, d) or a local
  path.

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• AS relationships
• The commercial agreements between pairs of
  administrative domains can be classified into
• customer-provider relationship
• peering relationship
• mutual-transit(sibling) relationship

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• Relationship between a pair of ASes
• customer-to-provider relationship
• provider-to-customer relationship
• peer-to-peer relationship
• sibling-to-sibling relationship

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BGP export rules
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• Lemma If u0s BGP routing table contains an
  entry with AS path (u1,u2,,un) for destination
  prefix d, then,
• (a) any node ui selects a route with as_path
  (ui1,,un) as the best route to prefix d, and,
• (b) ui exports its best route ui-1

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• Valley-free property
• After traversing a provider-to-customer or
  peer-to-peer edge, the AS path can not traverse a
  customer-to-provider or peer-to-peer edge.
• Formally, an AS path (u1,u2,,un) is valley-free
  iff the following conditions hold true
• A provider-to-customer edge can be followed by
  only provider-to-customer or sibling-to-sibling
  edges
• A peer-to-peer edge can be followed by only
  provider-to-customer or sibling-to-sibling edges

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• Theorem If all ASes set their export policies
  according to the BGP export rules, then an AS
  path in any BGP routing table entry is
  valley-free

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• An AS path of a BGP routing table entry has one
  of the following patterns
• an uphill path
• a downhill path
• an uphill path followed by a downhill path
• an uphill path followed by a peer-to-peer edge
• a peer-to-peer edge followed by a downhill path
• an uphill path followed by a peer-to-peer edge
  followed by a downhill path

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• Algorithm for inferring AS relationships
• Assume the pattern of routes in BGP routing
  table.
• Other intuition a provider typically has a
  larger size than its customer and the size of an
  AS is typically proportional to its degree in the
  AS graph
• top provider of an AS path is the AS that has the
  highest degree among all ASes in the path
• consecutive AS pairs on the left of the top
  provider are customer-to-provider or
  sibling-to-sibling edges and on the right are
  provider-to-customer or sibling-to-sibling edges
  

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• Inferring customer-provider, provider-customer,
  and sibling-sibling relations
• Input BGP routing table RT
• Output Annotated AS graph G
• Phase 1 Compute the degree for each AS
• Phase 2 Parse AS path to initialize consecutive
  AS pair relationship
• Phase 3 Assign relationship to AS pairs
• This is a heuristic that may generate
  inconsistent results.

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• Inferring peer-peer relation
• Peer-to-peer edge between top provider and one of
  its neighbors only
• If the top provider has sibling-to-sibling
  relationship with one of its neighbors, then it
  has a peer-to-peer relationship with the other
  neighbor
• We use the heuristic that peer-to-peer edge is
  between the top provider and its neighboring AS
  that has a higher degree because such edges are
  between ASes of comparable sizes
• We also use the heuristic that the degrees of two
  peers do not differ significantly - ASes having
  peer-to-peer relationship do not differ by more
  than R times

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• Final algorithm
• Input BGP routing table RT
• Output Annotated AS graph
• Phase 1 Use the algorithm to coarsely classify
  AS pairs into having provider-to-customer or
  sibling-to-sibling relationships
• Phase 2 Identify AS pairs that can not have a
  peer-to-peer relationship
• Phase 3 Assign peer-to-peer relationships from
  rest of the connected AS pairs as long as the
  pair degrees do not differ by more than R times