Internet Topology Mapping
Hakan Kardes
University of Nevada, Reno
Modified version of Dr. Gunes’s Presentation on Internet Topology Discovery
Outline

Introduction

Router Level Internet Topology Maps
• Topology Collection
• Topology Sampling
• Resolving Anonymous Routers
• Resolving Alias IP Addresses
• Resolving Genuine Subnets

Conclusion
Internet Topology Discovery
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Internet Measurements

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 Topology Discovery
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Internet Topology Measurement



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
Lumenta
CAIDAJan
Jan06
08
00
Internet Topology Discovery
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Router-Level Internet Topology Maps
Background

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.
2.
3.
4.
Sampling
Anonymous routers
Alias IP addresses
Subnet Inference
Internet Topology Discovery
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Topology Collection (traceroute)

Probe packets are carefully constructed to elicit intended
response from a probe destination
IPB
IPA
IPC
IPD
Vantage Point
Destination
TTL=1
TTL=2
TTL=3
TTL=4
S


A
B
C
D
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
Details
Internet Topology Discovery
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Topology Collection
e
f
Internet2 backbone
S
N
C
U
W
K
L
A
H
d
Internet Topology Discovery
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
7
Topology Sampling


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
Protocol
Responsiveness
ICMP
81.9 %
TCP
67.3 %
UDP
59.9 %
Approaches
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Anonymous Router Resolution
Problem

Anonymous routers do not respond to traceroute
probes and appear as  in traceroute output
•
Same router may appear as  in multiple traces.
y
y
y: S – L – H – x
y
y: S –  – H – x
S
SCurrent daily raw topology data sets
S include
• ~ 20 million path traces with
• ~ 20 million occurrences of s along with
L• ~ 500K public IP addresses L
1
The raw topology data is far from representing
the
H underlying sampled networkHtopology
x
x: H – L – S – y
x
x: H –  – S – y
Internet Topology Discovery
2
H
x
9
Anonymous Router Resolution
Problem
S
U
L
e
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
K
H
d
S
C
N
A
f
W
Sampled network
C
U
f
L
A
e
d
Internet Topology Discovery
W
Resulting network
10
Anonymous Router Resolution
Previous Approaches
Basic heuristics

•
•
IP: Combine anonymous nodes between same known nodes [Bilir 05]
•
Limited resolution
C
U
S
NM: Combine all anonymous neighborsL of a known node [Xin 06]
•
y
High false positives
More theoretic approaches
•
y
Graph minimization approach [Yao 03]
•
•
•
S
y
C
U
S

z
L
A
x
H
W
z
After W
resolution
A
Combine s as long as they do not violate two accuracy conditions:
x condition
After
(1) Trace preservation condition and (2) distance preservation
High complexity O(n5) – n is number of s
resolution
ISOMAP based dimensionality reduction approach [Xin 06]
C
z
S U
matrix
then use ISOMAP
to reduce it to a nx5 matrix
U• BuildKan nxn distance
N
C
z delay
Distance: (1) hop count or (2) link
W
y nodes L
• High complexity O(n3W
) – n is number of
H
A
L
A
x
Sampled network
Resulting network
x
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Anonymous Router Resolution
Graph Based Induction

A
x
y1
y2
y3
C



A
x
y1
y2
y3
C
Details
Parallel nodes
x
A
D
w
x
C
E
z
y
Clique
x

y

A
C


C
F
w

x
A
z
x
A

v

E
 
z
D
z
x
A



y
C
F
Details
Internet Topology Discovery
D
w
E
z
w

E
y
Star


Details
E
Complete Bipartite
D

w
C


y
D
A
C
D
E
v
Details
12
y
w
z
IP Alias Resolution
Problem
w
1
b 2
1 c
1
2 a
4
1
z
2
d
2
x
A set of collected traces

•
•
•
•
3
1
e
2
y
a sub-graph
w, …,b1, a1, c1, …, x
z, …,d1, a2, e1, …, y
x, …,c2, a3, b2, …, w
y, …,e2, a4, d2, …, z
Sample map from the collected path traces

A router
with different IP
in
b1 may appear
c1
d1 addresses
e1
a1
a2
different path
traces
•
w
x
z
Need to resolve
IP addresses belonging to the same
router
a3
a4
b2
c2
d2
y
e2
with no alias resolution
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IP Alias Resolution
Problem
S
U
K
C
N
f
Sampled network
L
e
H
A
W
d
s.3
u.1
k.1
c.1
n.1
u.2
k.2
c.2
n.2
s.1
e
f
s.2
w.3
l.1
l.3
n.3
a.3
h.2
h.1
h.4
Sample map
without alias resolution
d
Internet Topology Discovery
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.214- s.3 - e
IP Alias Resolution
Problem
1
w
b 2
1
2 a
4
1
z
2
1 c
z
x
3
2
d1
1
d
2
e
y
d2
b1
c1
a
w
sub-graph
x
b2
c2
a1
w
b
c
x
e1
e2
a2
a3
z
d
e
y
y
a4
partial alias resolution
(only router a is not resolved)
partial alias resolution
(only router a is resolved)
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IP Alias Resolution
Several Approaches



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 Bfield,
B
Many routers ignore direct probes.
Dest = A
DNS Based Method [Spring 04]
•
Relies on similarities in the host name structures
Dest = A
•

A
sl-bb21-lon-14-0.sprintlink.net
sl-bb21-lon-8-0.sprintlink.net
Dest = B
Works
when a systematic naming is used.
Dest = B
A, ID=100
B
A
BB,,ID=103
ID=99
Record Route Based Method [Sherwood 06]
•
Depends on router support to IP route record processing
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Genuine Subnet Resolution
Problem

Subnet resolution
•
Identify IP addresses that are connected over the same medium
IP1
IP1
IP2
IP3
IP2

IP3
Improve the quality of resulting topology map
A
C
B
D
(underlying topology)
A
B
A
C
D
CC
(observed topology)
Internet Topology Discovery
B B
A
D
D
(inferred topology)
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Conclusion

The Internet is man-made, so why do we need to measure it?
•
•
•

Because we still don’t 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
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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.
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Questions ?
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