Observations from Routerlevel Traces - PowerPoint PPT Presentation

Title: Observations from Routerlevel Traces


1
Observations from Router-level Traces

• Lisa Amini
• IBM T. J. Watson Research Center
• Joint with Henning Schulzrinne, Aurel Lazar
• Columbia University

2
Context

• Near-term issues facing service providers for
  Web-facing applications
• Mirrored servers
• where to place servers?
• which network access providers?
• how many connection points?
• how many servers to deploy?
• where to direct clients?
• End-to-end routing behavior/delay vs.
  connectivity
• AS level focus

3
Beyond Connectivity

• Inter-domain (AS) routing tables
• Aggregation
• Policy-based routing
• Oregon Route Server

Transit Networks
B
A
E
D
C
Autonomous Systems
Stub Networks
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Traceroute

• Router-level end-to-end probing
• Traceroute.org website
• AS lookup via Routing Arbiter Database (RADB)
• Round trip time (RTT)
• Loose source-routing
• Artifacts

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D1 Dataset

• 189 sites
• Random pairings
• Forward and reverse paths
• Poisson arrivals
• Mean time between probes 10 minutes
• 220,551 measurements
• 5 days
• 1/3 US sites, 2/3 non-US (31 countries)

• Zhang, Duffield, Paxson, Shenker

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Router-level Path Length

• mean16.45, std. dev.4.39

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AS Path Length

• mean6.47, std. dev.2.33

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AS Degree Frequency

• Faloutsos3 -0.97 (or higher) correlation
  coefficient
• 98 of nodes represented

0.97 correlation coefficient required discarding
31 of nodes
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Which is correct?
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AS Frequency
0.97 correlation coefficient required discarding
10 of nodes
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Response Time Prediction

• Does path length predict delay?

mean RTT263ms Correlation coefficient 0.31
Correlation coefficient 0.27
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AS Properties

• Can we predict delay based on AS path properties?
• Ranked each AS according to
• AS edge degree
• AS frequency
• Calculated mean RTT per path length
• Grouped by top 5, 6-10, 10-20 ASs

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Influence of Path Properties
High edge degree AS?
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High Frequency AS?
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High Edge Degree AS?
High edge degree AS in 2 AS hops?
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Backbone AS?
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Backbone AS in 2 AS hops?
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AS Affinity?
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Route Asymmetry

• Paxson, 1995
• Path(A,B) ? Path(B,A)
• Issues
• Ping triangulation
• Congestion Avoidance
• Internet mapping

A
B
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AS Hop Differences
11755 paired, unique routes 57 routes were
AS-path asymmetric Compare with 30 based on
1995 data 74 asymmetric from first AS hop
Number of Routes
Number of AS hop differences
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Traceroute Issues

• AS assignment
• Chang, Jamin, Willinger

AS6
AS5
AS7
AS1
AS2
AS3
AS4
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BGP AS Path

• Can we predict forward and reverse end-to-end
  metrics from BGP AS_PATH?
• Looking Glass Probing
• 92 Sites
• 8372 unique path measurements
• 2202 fully paired (BGP forward and reverse,
  traceroute forward and reverse)

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AS Hop Differences
47 of forward paths correctly predicted by
reverse traceroute 49 of forward paths
correctly predicted by reverse BGP AS_PATH 69
of forward paths correctly predicted by forward
BGP AS_PATH 34 asymmetry between
forward/reverse BGP AS_PATH
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Summary

• BGP routing tables provide complete view from
  single location.
• Aggregation
• Filtering
• End-to-end probing from points throughout network
  can provide insights beyond connectivity
• Limited view of connectivity
• Traceroute issues with noise, node assignment
• BGP AS_PATH inaccurate as path predictor

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Discard Criteria

• Origin traceroute server not responding
• Incomplete traceroute output
• Internal use only node address (e.g., 10.x.x.x,
  172.16.x.x-172.32.x.x ranges)
• Route did note terminate in target AS
• Intermediate node did not respond to ICMP echo
• No matching reverse probe for same time period

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What can we conclude?

• Results are for RTT only
• Negative results for
• Path Length
• AS degree, AS frequency, Backbone, hops from
  origin
• High delay as result of transient conditions
  (congestion)