Leveraging CDNs to Remotely Measure Network Distance · Use CDN replica selection •CDNs provide...
Transcript of Leveraging CDNs to Remotely Measure Network Distance · Use CDN replica selection •CDNs provide...
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Fury RouteLeveraging CDNs to Remotely
Measure Network Distance
Marcel FloresAlexander WenzelKevin ChenAleksandar Kuzmanovic
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Relative network distance• Which provider is closer
to the client?
• Enable systems to make a best-guess prior to the first communication.
• Can we do it without infrastructure or host participation?
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Client
Provider A
Provider B
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Relative network distance
• Peer and server selection.
• Large scale Internet measurement, allows understanding of hosts beyond control.
• Clients which can’t be subjected to direct measurements (i.e. traffic sensitive, unreachable).
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Use CDN replica selection• CDNs provide end users with a
“nearest” replica.
• Helps to reduce user-experienced latency.
• Often selected via DNS.
• Providers include: Google, Edgecast, Alibaba, CDN77, CloudFront, CDNetworks, Adnxs
• Varying response granularity
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EDNS Client Subnet• Allows DNS requests to include an origin subnet.
• Simplifies replica selection procedure.
• Further provides a scope, indicating the specificity of the response.
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Allows for queries as arbitrary hosts.
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Build a graph• Construct a directed graph G = (V, E)
• V = Set of hosts (client, provider, replicas)
• E = Set of of CDN replica response relationships
• weight(A, B) = 32 - scope (a, b)
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10CDN Responses}
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Build a graph
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Arizona
Rutgers
Cloudfront - LAX
Google - DFW
88 Google - LGA
CDN77 - NY
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Forward progress• How do we know which candidate to select?
• Ask coarse-grained providers which replica they would serve to each candidate.
• Further ask which replicas they would serve the target set.
• Measure the overlap in responses.
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Build a graph
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Arizona
Rutgers
Cloudfront - LAX
Google - DFW
88 Google - LGA
CDN77 - NY
10
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Build a chain
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Arizona
Rutgers
Cloudfront - LAX
Google - DFW
88
Google - LAX
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Google - LGA
CDN77 - NY
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UCLA
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Why does it work?• Ultimately reveals the underlying infrastructure of
the CDN Deployments.
• Low-density deployments will indicate large distances.
• Not all deployments are the same.
• ECS responses are more than just noise.
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Accuracy
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Origin
Targets1) Measure ping time
2) Construct chains
3) Compare pairs
4) Count matches
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Accuracy
• Filter by minimum difference:
• All, 25, 50, 100ms differences.
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21 75
• What about very similar distances?
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Accuracy
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Median 83% correct
Best
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Caching• Would like to build a consistent graph that expands
as we see more hosts.
• How significantly does this graph actually reduce the queries?
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Caching
After 20 paths, chains complete with under 50 queries18
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Summary
• Developed a system which provides an estimate of relative network distance.
• Correctly determines 83% of relative distances in the median case.
• After a cache is established, the majority of chains can be built with under 50 queries.
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Thank you!