Path Diversity ! Number of paths for a packet to transit between two - - PDF document

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In Search for Path Diversity in ISP Networks

Renata Teixeira, Keith Marzullo, Stefan Savage, Geoffrey M. Voelker UC San Diego Internet Measurement Conference 2003

IMC’2003 2

Path Diversity

! Number of paths for a packet to transit between two points

" Inside an autonomous system network (ISP) " Fully link and PoP (Point of Presence) disjoint paths " Observed at IP level

! Applications

" Robustness, resilience to failures " Traffic engineering

! How much path diversity is there in real networks?

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IMC’2003 3

Path Diversity inside an AS

Rio de Janeiro São Paulo Brasília Recife Point of Presence (PoP) Link-disjoint paths PoP-disjoint paths Given an ISP network topology, use standard graph algorithms to compute path diversity.

IMC’2003 4

Topologies Studied

! Inferred topologies (Rocketfuel)

" Nine router-level ISP topologies (incl. Sprint) " Reconstruct PoP-level topology

! Exact Sprint network topology

" PoP-level topology of the continental US

backbone network

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IMC’2003 5

Inferring ISP Topology

traces Inferred ISP Topology ISP Network processing

• Clean-up traces
• Collapse interfaces into routers
• Insert reverse edges

probing

• Choose vantage points and destinations
• Perform a set of traceroutes

IMC’2003 6

Path Diversity in Inferred Sprint Topology

Inferred C u m u l a t i v e f r a c t i

• n
• f

p a i r s

• f

P

• P

s Number of link-disjoint paths At least five link-disjoint paths between all pairs of PoP

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IMC’2003 7

Inferred vs. Exact Path Diversity

Inferred C u m u l a t i v e f r a c t i

• n
• f

p a i r s

• f

P

• P

s Number of link-disjoint paths C u m u l a t i v e f r a c t i

• n
• f

p a i r s

• f

P

• P

s Number of link-disjoint paths Exact Inferred There are at least four link-disjoint paths between almost 90% of pairs of PoPs Inferred topology has 1.25 to 4.4 times more link-disjoint paths

IMC’2003 8

Accuracy of Inferred Sprint Topology

traces Inferred Sprint Topology Exact Sprint Topology Links:

• Missed: 8.57%
• Added: 608.57%

processing probing

• Missed: 58.57%
• Added: 37.14%
• Missed: --
• Added: 717.14%
• Lack of vantage points
• Incomplete traceroutes
• Changes in the path

during a probe

• Obsolete DNS
• Incorrect alias resolution
• Adding reverse links

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IMC’2003 9

Summary

! Large diversity in path diversity!

" Depends on network design

! High level of path diversity in Sprint network

" 90% of PoP-pairs have at least 4 link-disjoint paths

! Extracting path diversity is challenging

" Inferred topologies are not representative of path

diversity

" Getting real data is unrealistic IMC’2003 10

Warning

Inferred topologies should be used carefully!

" Need to understand limitations of the data " Impact on relevant topological properties