1 Seminar / Summer Semester 2000 Internet Connectivity Christian A. Plattner,

2 Internet Connectivity On Power-Law Relationships of the Internet Topology End-to-End Routing Behaviour in the Internet

3 Power-Laws of the Internet What does the Internet look like? Are there any properties that don’t change in time? How will it look like a year from now? How can I generate Internet-like graphs for my simulations?

4 Benefits from Understanding the Topology of the Internet Protocol design More accurate artificial models Estimates for topological parameters

5 Internet Topology Two different views: router level vs. interdomain level Partitioning the network into AS‘s Intra- vs. Inter-AS routing

6 Router- vs. Interdomain-level Domain 2 Domain 3 Domain 1

7 AS Example: UUnet

8 Power-Laws of the Internet Power-Law 1:d v  r v R Power-Law 2:f d  d O Hop-plot exponent:P(h)  h H Edges:E = N/(2R + 2) (1-1/N R+1 ) Diameter :  = (N 2 / N + 2E) 1/ H

9 Practical Uses of the Power-Laws Describing graphs Protocol performance Graph generation and selection Predictions and extrapolations Year Nodes Edges d

10 End-to-End Routing Behaviour in the Internet What sorts of pathologies and failures occur in the Internet? Do routes remain stable over time or change frequently? Do routes from A to B tend to be symmetric as routes from B to A?

11 But we know the protocols very well... Distinction between protocols and behaviour is important! It’s not obvious how the backbone dynamics translate into the routing dynamics seen by an end user

12 Methodology Measurement of a large sample of Internet routes Measurements were done in two different periods Measuring instrument: traceroute

13 The Design of the Experiment Network probe daemon Npd_control Key property: N 2 scaling

14 How representative can the Observations be ? About 30 Internet hosts participated 1995: 6.6 million Internet hosts! About 1000 active AS’s in 1995

15 The Experiment D1: November 8 through December 24, 1994 D2: November 3 through December 21, 1995 Main difference: D2 consists of paired traceroutes

16 Routing Pathologies Routing loops Erroneous routing Connectivity altered mid-stream Fluttering Infrastructure failures Unreachable due to many hops Temporary outages

17 Summary of Routing Pathologies PathologyProbabilityTrend Persistent loops % Erroneous routing % Mid-stream change 0.16%  0.44% worse Infrastructure failure 0.21%  0.48% worse Outage >= 30 secs 0.96%  2.2% worse Total pathologies 1.5%  3.3% worse

18 End-to-End Routing Stability Two definitions of stability: · Routing prevalence · Routing persistence

19 Routing (A)symmetry One-way propagation time Anticipatory flow state Network troubleshooting Causes of routing asymmetries?

20 Summary Overwiew of the Internet topology Power-Laws of the Internet and their practical use End-to-end routing behaviour