Network Topology Measurement

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Network Topology Measurement

• Yang Chen
• CS 8803

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Outline

• Big Picture
• ISP Topology Measurement
• Statistical Results
• Problems Solutions

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Heuristics for Internet Map Discovery

• R. Govindan and H. Tangmunarunkit
• INFOCOM 2000

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Why do we need the topology?

• Understand the macroscopic properties of the
  Internet physical structure
• Network management
• Topology-aware algorithms
• Simulation and topology generation tools

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On-going efforts

• CAIDA Skitter

• Router View

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Fundamental traceroute
Prober sends packets with successively increased
TTL. A router responds with ICMP time exceeded
when the probe is with TTL1
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Fundamental traceroute
Geographic info can help on building up the
topology.
Data from http//www.linkwan.com/vr/
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Fundamental Tree gt map

1. Source routing
2. Multiple Vantage points

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Address scan space

• BGP tables
• Route Table
• Database
• Informed Random Address Probing
• A response from some IP address is considered as
  a sign that some prefix P of A must contain
  addressable nodes
• If P is an addressable prefix, the neighboring
  prefixes of P are also considered as possibly
  addressable. (128.8/16 and 128.10/16 are
  neighbors of 128.9/16)

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Some results

• 150,000 interfaces and nearly 200,000 links
• Findings related to source route
• Simulation demonstrated that In relatively sparse
  random networks, a few source route capable nodes
  (lt 5) are sufficient to discover 90 of the
  links. In fact, there are 8 routers support
  source route.
• Source route discovered links do not skew the
  qualitative conclusion on the network statistics.
  

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For example degree distribution
Similar observation on hop-pair distribution
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Measuring ISP Topologies with Rocketfuel

• N.Spring, R. Mahajan and D. Wetherall
• ACM Sigcomm 2002

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ISP network infrastructure
Access Router
Access Router
Backbone Router
Backbone Link
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ISP topology measurement

• An old story the blinds and the elephant

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ISP topology measurement
Traceroute Server
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Focusing on one ISP Directed probing
Network Next Hop M/LP/Weight
Path 192.9.9.0 204.212.44.128
0 234 266 237 3561 701 90 i
205.238.48.3 0 2914 1 90 i
144.228.240.93 0
1239 701 90 i 204.70.4.89
0 3561 1 90 i
194.68.130.254 0 5459 5413 1 90 i
gt 134.24.127.3 0
1740 701 90 i 202.232.1.8
0 2497 701 90 i
158.43.133.48 0 1849 702 701 90 i
131.103.20.49 0
1225 2548 1 90 i
blackrose.org (Ann Arbor) 204.212.44.128
through AS234 Verio (MAE-WEST)
205.238.48.3 through AS2914 Sprint
(Stockton) 144.228.240.93 through AS1239
MCI (San Francisco) 204.70.4.89
through AS3561 LINX (London)
194.68.130.254 through AS5459 CERFnet
(San Diego) 134.24.127.3 through AS1740
IIJ (Japan) 202.232.1.8
through AS2497 PIPEX (London)
158.43.133.48 through AS1849 IAGnet
(Chicago) 131.103.20.49 through AS1225
BGP table source RouteView project
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Focusing on one ISP Directed probing

• Traceroutes to dependent prefixes All
  traceroutes to these prefixes from any vantage
  point should transit the ISP. Dependent prefixes
  can be readily identified from the BGP table. All
  AS-paths for the prefix would contain the number
  of the AS being mapped.
• Traceroutes from insiders We call a traceroute
  server located in a dependent prefix an insider.
  Traceroutes from insiders to any prefix should
  transit the ISP.
• Traceroutes that are likely to transit the ISP
  based on some AS-path are called up/down traces.

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Path/Query reduction
Share Ingress
Share egress
Same next-hop AS number
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Impacts of directed probing

1. Fraction of useful but pruned traces from 0.1 to
   7
2. Unnecessary traces around 6 over all the ISPs

Comparison based on Skitter data
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Impacts of ingress reduction
Overall, ingress reduction keeps only 12 of the
traces chosen by directed probing.
The number of vantage points that share an
ingress by rank
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Impacts of egress reduction
Overall, egress reduction keeps only 18 of the
Dependent prefix traces chosen by directed
probing.
The number of dependent prefixes that share an
egress by rank
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Impacts of next-hop reduction
Overall, Next-hop AS reduction Reduces the
number of traces to 5 of those chosen by
directed probing.
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POP sizes analysis
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Power Law

• Complementary cumulative distribution function
  (CCDF) P(Xgtx)
• Pareto Distribution
• Power Law

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Router degree distribution
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Peering structure
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Difficulties in topology discovery

• Shared media
• Backup links
• Router Identification and annotation
• Alias resolution
• Completeness Validation
• Currently, none of them is completely solved!

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POP hierarchy
Naming convention, DNS information and neighbor
inferring
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Backbone topology
ATT
Level 3
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Alias Problem
OR
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Alias is it a big deal?
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Alias resolution

• Send a packet with unreachable port to certain
  interfaces which are possible alias. The
  corresponding ICMP port unreachable response will
  contain the source address.
• IP identifier

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Completeness validation

• Comparison with Router Views
• Comparison with Skitter
• IP address space
• Search prefixes of ISPs address space for
  additional IP addresses
• Validation with ISPs
• Is Good enough?

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In Search of Path Diversity in ISP Networks

• P. Teixeira, K. Marzullo, S. Savage and G. M.
  Voelker
• IMC 2003

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Real metric instead of counting links

• Path diversity
• Metric that reflects the number of routes
  available between two points in the network
• An extreme example

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Real topology speaks
Inter-PoP Path diversity in the Sprint
Network
Inter-PoP Path diversity inferred
by Rocketfuel
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Take a closer look
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Inaccuracy introduced during probing

• Lack of vantage points
• How many points are sufficient?
• Incomplete traceroutes
• What can we do if ISP turns off traceroute
  functionality?
• Changes in the path of a probe
• Incorrect DNS record

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Inaccuracy from processing probed links

• Alias Resolution
• Adding reverse links

Missed and added links in Rocketfuel PoP topology
relative to the number of links in the
Sprintreal topology
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Questions?