Internet Topology Mapping Hakan Kardes University of Nevada,
Reno Modified version of Dr. Guness Presentation on Internet
Topology Discovery
Slide 2
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
Slide 3
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
Slide 4
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
Slide 5
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
Slide 6
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
Slide 7
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
Slide 8
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
Slide 9
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
Slide 10
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
Slide 11
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
Slide 12
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
Slide 13
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
Slide 14
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
Slide 15
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
Slide 16
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
Slide 17
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
Slide 18
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
Slide 19
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