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Internet Topology Mapping Hakan Kardes University of Nevada, Reno Modified version of Dr. Guness Presentation on Internet Topology Discovery

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Outline Introduction Router Level Internet Topology Maps Topology Collection Topology Sampling Resolving Anonymous Routers Resolving Alias IP Addresses Resolving Genuine Subnets Conclusion 2 Internet Topology Discovery

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Understand topological and functional characteristics of the Internet Essential to design, implement, protect, and operate underlying network technologies, protocols, services, and applications Need for Internet measurements arises due to commercial, social, and technical issues Realistic simulation environment for developed products, Improve network management Robustness with respect to failures/attacks Comprehend spreading of worms/viruses Know social trends in Internet use Scientific discovery Scale-free (power-law), Small-world, Rich-club, Dissasortativity, Internet Measurements 3 Internet Topology Discovery

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Types of Internet topology maps Autonomous System (AS) level maps Router level maps A router level Internet map consists of Nodes: End-hosts and routers Links: Point-to-point or multi-access links Router level Internet topology discovery A process of identifying nodes and links among them Internet Topology Measurement 4 Internet Topology Discovery Lumenta Jan 06CAIDA Jan 08CAIDA Jan 00

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Internet topology measurement studies Involves topology collection / construction / analysis Current state of the research activities Distributed topology data collection studies/platforms iPlane, Skitter, Dimes, DipZoom, 20M path traces with over 20M nodes (daily) Main Issues 1.Sampling 2.Anonymous routers 3.Alias IP addresses 4.Subnet Inference Router-Level Internet Topology Maps Background 5 Internet Topology Discovery

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Probe packets are carefully constructed to elicit intended response from a probe destination traceroute probes all nodes on a path towards a given destination TTL-scoped probes obtain ICMP error messages from routers on the path ICMP messages includes the IP address of intermediate routers as its source Merging end-to-end path traces yields the network map S DABC Destination Topology Collection (traceroute) TTL=1 IP A TTL=2 IP B TTL=3 IP C TTL=4 IP D Vantage Point 6 Internet Topology Discovery Details

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Topology Collection Internet2 backbone Traces d - H - L - S - e d - H - A - W - N - f e - S - L - H - d e - S - U - K - C - N - f f - N - C - K- H - d f - N - C - K - U - S - e S L U K C H A W N e d f 7 Internet Topology Discovery

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8 Sampling to discover networks Infer characteristics of the topology Different studies considered Effect of sample size [Barford 01] Sampling bias [Lakhina 03] Path accuracy [Augustin 06] Sampling approach [Gunes 07] Utilized protocol [Gunes 08] ICMP echo request TCP syn UDP port unreachable ~ 10% of routers are anonymous Topology Sampling Internet Topology Discovery ProtocolResponsiveness ICMP81.9 % TCP67.3 % UDP59.9 % Approaches

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Anonymous routers do not respond to traceroute probes and appear as in traceroute output Same router may appear as in multiple traces. 9 Anonymous Router Resolution Problem y: S L H x x: H L S y y: S H x x: H S y S L H y x S L H y x y S 11 22 H x Internet Topology Discovery Current daily raw topology data sets include ~ 20 million path traces with ~ 20 million occurrences of s along with ~ 500K public IP addresses The raw topology data is far from representing the underlying sampled network topology

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Anonymous Router Resolution Problem UKCN LHAW S d e f Sampled network d e f S U L C A W Resulting network 10 Internet Topology Discovery Traces d - - L - S - e d - - A - W - - f e - S - L - - d e - S - U - - C - - f f - - C - - - d f - - C - - U - S - e

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11 Anonymous Router Resolution Previous Approaches Basic heuristics IP: Combine anonymous nodes between same known nodes [Bilir 05] Limited resolution NM: Combine all anonymous neighbors of a known node [Xin 06] High false positives More theoretic approaches Graph minimization approach [Yao 03] Combine s as long as they do not violate two accuracy conditions: (1) Trace preservation condition and (2) distance preservation condition High complexity O(n 5 ) n is number of s ISOMAP based dimensionality reduction approach [Xin 06] Build an n x n distance matrix then use ISOMAP to reduce it to a n x 5 matrix Distance: (1) hop count or (2) link delay High complexity O(n 3 ) n is number of nodes UK C N L HA W S x y z Sampled network x y z S U L C A W After resolution x y z S U L C A W H x y z S U L C A W Resulting network Internet Topology Discovery

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12 Anonymous Router Resolution Graph Based Induction Parallel nodes A x C y2 y1 y3 A x C y2 y1 y3 Star DA wx C y E z DA wx C y E z Complete Bipartite A C x y D w F v E z A C x y D w F v E z Clique A C x y D w E z A C x y D w E z Internet Topology Discovery Details

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IP Alias Resolution Problem a c d b e a sub-graph a1 c1 b2 b1 c2 with no alias resolution w zy x A set of collected traces w, ,b1, a1, c1, , x z, ,d1, a2, e1, , y x, ,c2, a3, b2, , w y, ,e2, a4, d2, , z xw a3 a2 e1 d2 d1 e2 yz a4 Sample map from the collected path traces 1 3 4 1 1 1 1 2 2 2 2 2 Internet Topology Discovery 13 A router may appear with different IP addresses in different path traces Need to resolve IP addresses belonging to the same router

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14 IP Alias Resolution Problem Internet Topology Discovery UKCN LHAW S d e f Sampled network Sample map without alias resolution s.3 s.1 s.2 l.3 l.1 u.1 u.2 k.1 c.1n.1 n.2 k.2 c.2 w.3 a.3 h.2 h.4 h.1 e d f n.3 Traces d - h.4 - l.3 - s.2 - e d - h.4 - a.3 - w.3 - n.3 - f e - s.1 - l.1 - h.1 - d e - s.1 - u.1 - k.1 - c.1 - n.1 - f f - n.2 - c.2 - k.2 - h.2 - d f - n.2 - c.2 - k.2 - u.2 - s.3 - e

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IP Alias Resolution Problem a c1 b2 b1 c2 partial alias resolution (only router a is resolved) x w e1 d2d1 e2 y z partial alias resolution (only router a is not resolved) a2 c d b e w zy x a3 a4 a1 15 Internet Topology Discovery a c d b e sub-graph w zy x 1 3 4 1 1 1 1 2 2 2 2 2

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16 IP Alias Resolution Several Approaches Dest = A B Dest = B A, ID=100 Dest = B B, ID=99 B, ID=103 A B A B Source IP Address Based Method [Pansiot 98] Relies on a particular implementation of ICMP error generation. IP Identification Based Method (ally) [Spring 03] Relies on a particular implementation of IP identifier field, Many routers ignore direct probes. DNS Based Method [Spring 04] Relies on similarities in the host name structures sl-bb21-lon-14-0.sprintlink.net sl-bb21-lon-8-0.sprintlink.net Works when a systematic naming is used. Record Route Based Method [Sherwood 06] Depends on router support to IP route record processing Internet Topology Discovery

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17 Genuine Subnet Resolution Problem Subnet resolution Identify IP addresses that are connected over the same medium Improve the quality of resulting topology map IP2 IP3 IP1 IP2IP3 IP1 Internet Topology Discovery (observed topology)(inferred topology)(underlying topology) CD AB CD AB CD AB CD AB

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18 Conclusion The Internet is man-made, so why do we need to measure it? Because we still dont really understand it Sometimes things go wrong Measurement for network operations Detecting and diagnosing problems What-if analysis of future changes Measurement for scientific discovery Creating accurate models that represent reality Identifying new features and phenomena Researchers have been sampling and analyzing Internet topology Building network graph from raw-data was not handled carefully Many researchers pointed out issues due to sampling and developed algorithms to handle each of them Resolving anonymous routers, IP aliases, and genuine subnets Huge computational and probing overhead due to very large data size Internet Topology Discovery

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19 References 1.M.H. Gunes, S. Bilir, K. Sarac and T. Korkmaz, A Measurement Study on Overhead Distribution of Value-Added Internet Services, Computer Networks 2007. 2.M.H. Gunes and K. Sarac, Resolving IP aliases in Building Traceroute-Based Internet Maps, IEEE Transactions on Networking (to appear). 3.M.H. Gunes, M. Baysan and K. Sarac, Resolving Anonymous Routers in Building Traceroute-Based Internet Maps, IEEE Transactions on Networking (in preperation). 4.M.H. Gunes and K. Sarac, Analytical IP Alias Resolution, IEEE ICC 2006. 5.M.H. Gunes, N.S. Nielsen and K. Sarac Impact of IP alias resolution on Traceroute-Based Sample Network Topologies, PAM 2007. 6.M.H. Gunes and K. Sarac, Importance of IP alias resolution in Sampling Internet Topologies, IEEE GI 2007, 7.M.H. Gunes and K. Sarac, Inferring Subnets in Router-level Topology Collection Studies, ACM SIGCOMM IMC 2007. 8.M.H. Gunes and K. Sarac, Resolving Anonymous Routers in Internet Topology Measurement Studies, IEEE INFOCOM 2008. Internet Topology Discovery

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Questions ? Internet Topology Discovery 20