Internet and Overlay Networks

1
Internet and Overlay Networks

• Ram Keralapura
• ECE Dept
• rkeralapura_at_ucdavis.edu

2
Layered Architecture

• Five main layers
• Application layer
• Transport layer
• Network (IP) layer
• Link layer
• Physical/Optical layer

Applications/Computers Application layer links
Routers Virtual IP links
Optical switches Optical fibers
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Introduction

• Internet Routing Infrastructure
• Intra-domain routing (IGP)
• RIP, OSFP, ISIS, etc.
• Inter-domain routing
• BGP

Internet
Domain or Autonomous System
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Intra-domain Routing

• Links are assigned link costs/weights
• Path between two nodes inside a domain follows
  shortest path (least cost path)

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Network Properties

• Important properties of networks that service
  providers look for
• Connectivity
• Performance
• Resiliency
• Robustness in functionality
• Service availability delivering a given packet
  from source to destination

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Characterizing Networks

• Main causes for concern resiliency and
  robustness
• How does the IGP protocol behave during network
  component failures?
• How does the behavior impact the data that the
  network carries?

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Characterizing Networks (contd)

• We have developed a model that captures the
  dynamic behavior of the network protocols during
  link failures Keralapura et al, 2004
• Protocol convergence depends on
• Topology nodes and connectivity
• Protocol timer settings
• Number of entries to update in the forwarding
  tables

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Characterizing Networks (contd)

• Metrics for service availability
• Service disruption time
• Traffic disruption
• Based on the above metrics we define goodness
  factor for the network

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Results (contd)
Ingress Node Goodness
Static properties (like node out-degree) do not
capture operational conditions and network
dynamics
Out Degree
Ingress Node Goodness
Out Degree
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Network Goodness
Network Diameter
Similar results were also found in the paper
Layered Complex Networks by Kurant and Thiran
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Internet Architecture

• Tiered hierarchy in domains

Peering relationship
Tier-1 B
Tier-1 A
Tier-2 C
Tier-2 D
Tier-2 F
Tier-2 E
Customer-Provider relationship
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Inter-domain routing

• Policy-based routing
• Ad-hoc and can change with agreements with other
  domains
• Can we capture these policies?
• Domains do not disclose their connectivity
• Policies can obstruct views and hinder
  domain-level topology discovery
• Need multiple vantage points for more accurate
  topology information

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Application Layer Networks

• Email Networks
• World Wide Web (WWW)
• Peer-to-Peer (p2p) Networks
• Several Content Delivery Networks (CDN)

Overlay networks
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Background Overlay Networks
B
D
Domain-2
A
B
Y
X
D
C
A
Domain-4
Domain-1
Domain-3
C
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Interaction between networks

• Overlay networks compete with IP networks to
  provide routing service
• IP and overlay networks are unaware of key things
  happening at the other layer
• Multiple overlay networks co-exist and make
  independent decisions
• How does all this affect IP and overlay networks?

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Interactions between Networks

• Identified some potential interactions
  Keralapura et al, 2005
• Traffic engineering in IP networks
• Load balancing issues
• IP layer traffic matrix estimation
• Coupling of multiple domains
• Defeats the objective of BGP
• Multiple co-existing overlay networks
• Traffic oscillations
• Cascading reactions

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Load Balancing and TM Estimation
F
5
5
G
H
5
5
5
8
N
M
5
A
E
20
5
8
5
5
B
D
5
5
C
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Coupling Multiple AS Domains
F
B
X
G
C
E
A
H
D
Domain-2
Domain-1
Defeats one of the objectives of BGP to decouple
different domains
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Traffic Oscillations
Traffic Oscillations
Failure of link 10-12
Failure of link 2-5
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Open questions

• Interactions need to be understood better and we
  need to model them
• How to go about characterizing the robustness of
  a network after we model such interactions?
• Are there interactions between networks at other
  layers?
• If yes, then how to we qualify, quantify, and
  model them?