Router-level
Internet Topology Mapping
By Talha OZ
Outline

Introduction

Internet Topology Collection
•
•
•

Basic Techniques
Some Measurement Projects & Platforms
Issues in Topology Collection
Issues in Topology Construction
•
•
•

My stress on this presentation
Will be explained in detail
in the next presentation
Resolving Anonymous Routers
Resolving Alias IP Addresses
Resolving Genuine Subnets
Summary
Internet Topology Discovery
2
Outline

Introduction
•
•

Internet Topology Collection
•
•
•

Basic Techniques
Some Measurement projects & platforms
Issues in Topology Collection
Issues in Topology Construction
•
•
•

Internet as a Complex Network
Motivations on Internet Topology Measurement
Resolving Anonymous Routers
Resolving Alias IP Addresses
Resolving Genuine Subnets
Summary
Internet Topology Discovery
3
Internet

Web of interconnected networks
•
•
•
•
Grows with no central authority
Autonomous Systems optimize local communication efficiency
The building blocks are engineered and studied in depth
Global entity has not been characterized

Most real world complex-networks
have non-trivial properties.

Global properties can not be inferred from local ones
•
•
Engineered with large technical diversity
Range from local campuses to transcontinental backbone
providers
Internet Topology Discovery
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Motivation on
Internet Topology Measurement

Once the graph is built, one can study its characteristics
•
Essential to design, implement, protect, and operate underlying network
technologies, protocols, services, and applications

Capture graph’s theoretic resilience to failure or say something about its
efficiency for routing

Realistic simulation environment for developed products

Comprehend spreading of worms/viruses (Burch and Cheswick’s proposal)

Improve QoS for the multimedia content

•
Where to store the data in replicated servers distributed across the internet
ISPs are not willing to share their topology information
Lumenta Jan 06
Internet Topology Discovery
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Internet Topology Measurement
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
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Types of Internet topology maps
•
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Autonomous System (AS) level maps
Point of presence (PoP) level
Router level maps
IP interface level
A router level Internet map consists of
•
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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
6
Outline

Introduction

Internet Topology Collection
•
•
•

Some Measurement projects & platforms
Issues in Topology Collection
Issues in Topology Construction
•
•
•

Basic Techniques
Resolving Anonymous Routers
Resolving Alias IP Addresses
Resolving Genuine Subnets
Summary
Internet Topology Discovery
7
Internet Topology Measurement
Topology Collection

Internet topology measurement studies


Involves topology collection / construction / analysis
How to collect ?




Work on IP layer, leverage header information
IETF’s RFCs determine the behavior of the nodes
Send ICMP, UDP, TCP packets and wait ...
Ideal case and issues ...
Internet Topology Discovery
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Internet Topology Measurement
Topology Collection – Who sets the rules ?

IETF
The Internet Engineering Task Force (IETF)
develops and promotes Internet standards

RFC
An Internet Standard is a special Request for
Comments (RFC) or set of RFCs.

http://tools.ietf.org/html/rfc792
Internet Topology Discovery
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Internet Topology Measurement
How to collect
Internet Topology Discovery
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Internet Topology Measurements
Probing

Direct probing
IPB
IPD
Vantage Point
IPBD TTL=64
A

B
C
D
Indirect probing
IPB
IPC
Vantage Point
IPD TTL=1
TTL=2
A
B
C
Internet Topology Discovery
D
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Internet Topology Measurement
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
Internet Topology Discovery
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Internet Topology Measurement:
Background
Internet2 backbone
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Trace to Seattle
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Internet Topology Mapping
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Internet Topology Measurement:
Background
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Internet Topology Mapping
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Internet Topology Measurement
Topology Collection
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Internet2 backbone
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Internet Topology Discovery
Traces
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• f - N - C - K- H - d
•f-N-C-K-U-S-e
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Outline

Introduction

Internet Topology Collection
•
•
•

Some measurement projects & platforms
Issues in Topology Collection
Issues in Topology Construction
•
•
•

Basic Techniques
Resolving Anonymous Routers
Resolving Alias IP Addresses
Resolving Genuine Subnets
Summary
Internet Topology Discovery
16
Topology Data Collecting Platforms - I

PlanetLab
•
•
Currently consists of 1020 nodes at 483 sites
Since the beginning of 2003, 1000+ researchers develop new
technologies for
•
•
•
•
•

distributed storage
network mapping
peer-to-peer systems
distributed hash tables
query processing
CAIDA (Cooperative Association for Internet Data Analysis)
•
•
Provides tools and analyses promoting the engineering and
maintenance of a robust, scalable global Internet infrastructure.
San Diego Supercomputer Center @ UCSD
Internet Topology Discovery
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Topology Data Collecting Platforms - II

Macroscopic Topology Measurements (Skitter project)
by CAIDA
•
•
•

characterize macroscopic connectivity and performance of the
Internet
allow various topological and geographical representations at
multiple levels of aggregation granularity
provide a valuable input for empirically-based modeling of the
Internet behavior and properties
Skitter, developed by CAIDA
•
•
skitter measurement tool reads a file of destinations and writes
a file of traceroute paths
...
Internet Topology Discovery
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Topology Data Collecting Platforms - III
•
•
•
•
•
•

...
ICMP traceroutes are used
RTTs are also stored
24 monitors around the world
970K common destination, IPv4 addresses
Scamper does the similar thing for IPv6
Archipelago (Ark) is the evolution of the
skitter infrastructure, by CAIDA
•
•
•
•
skitter monitors
skitter measurement tool
an internal web server for distributing destination lists
a file storage server for collecting traces from monitors
Internet Topology Discovery
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Topology Collecting Platforms - IV

The Distributed Internet Measurements and Simulations
(DIMES)
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•
•

Model of SETI@home
Counts more than 20,343 agents scattered over five continents
“What we ask is not so much your CPU or bandwidth (which we
hardly consume), but rather, your location.”
iPlane
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Measuring the Internet: performs traceroutes from various VPs
-- PlanetLab nodes and traceroute servers -- to construct a
router interface-level atlas of the Internet.
Clustering interfaces into PoPs
Measuring link attributes
Opportunistic measurements
Route prediction
Internet Topology Discovery
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Topology Collecting Platforms - V

Rocketfuel tries to get the picture of the ISPs
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•
•
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Number of required probes is decreased
•
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directed probing
path reduction (ingress & egress)
Alias resolution
Router identification and annotation (DNS and ISP naming)
Report on properties of maps from ten diverse ISPs :
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Size of POPs
Distribution of router outdegree
Inter-domain peering structure
Internet Topology Discovery
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Topology Collecting Platforms - VI
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Scriptroute allows everyone to measure from several VPs
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Proposes remote measurement execution on PlanetLab nodes
RPT tool avoids retracing paths
TTM, developed by RIPE NCC
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Full mesh between roughly a hundred monitors
One-way delay, packet loss, and bandwidth are also stored
Atlas is based on “source-routed IPv6 traceroute”
•
probe engine, topology constructor, topology verifier, interactive
visualization program
Internet Topology Discovery
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Topology Collecting Platforms - VII

TCP Sidecar
•
•
•

a technique and associated API for embedding measurement
probes into non-measurement TCP streams
avoids abuse reports and allows measurements to tunnel through
NATs and behind firewalls
Augment traceroute (TR) probes with IP Record Route option (RR)
DipZoom (Deep Internet Performance Zoom)
•
•
•
Focused, on-demand Internet measurements
Offers a matchmaking service which uses P2P concepts to bring
together experimenters in need of measurements with external
measurement providers.
DipZoom participants offer measurements for the benefit of being
able to access measurements offered by other participants
Internet Topology Discovery
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Outline

Introduction

Internet Topology Collection
•
•
•

Some measurement projects & platforms
Issues in Topology Collection
Issues in Topology Construction
•
•
•

Basic Techniques
Resolving Anonymous Routers
Resolving Alias IP Addresses
Resolving Genuine Subnets
Summary
Internet Topology Discovery
24
Issues in Topology Collection
Issues I

Forward & primary paths
•
•
Asymmetric routing
miss out on backup paths

Unbiased Sampling

Traceroute & load balancer (Paris traceroute)

MPLS (TTL reduction)

Misconfigurated network elements
Internet Topology Discovery
25
Issues in Topology Collection
Issues II

Third-party address (multi homing)

Redundancy

•
•
•
intra-monitor redundancy
inter-monitor redundancy
DDoS
Responsiveness
•
•
•
ICMP echo request
TCP syn
UDP port unreachable
Internet Topology Discovery
26
Outline

Introduction

Internet Topology Collection
•
•
•

Some measurement projects & platforms
Issues in Topology Collection
Issues in Topology Construction
•
•
•

Basic Techniques
Resolving Alias IP Addresses
Resolving Anonymous Routers
Resolving Genuine Subnets
Summary
Internet Topology Discovery
27
Issues in Topology Construction - I
at Router Level

Alias Resolution
•
•
•
•
•
•
Iffinder
Ally
DNS based method
Graph based method
Analytical IP Alias Resolution (APAR)
Record route option
Internet Topology Discovery
28
Alias Resolution




Each interface of a router
has an IP address.
A router may respond with
different IP addresses to
different queries.
.33
.5
.18
Denver
.7
.13
Alias Resolution is the process of grouping the interface
IP addresses of each router into a single node.
Inaccuracies in alias resolution may result in a network
map that
•
•
includes artificial links/nodes
misses existing links
Internet Topology Discovery
29
Issues in Topology Construction - II
at Router Level

Anonymous Router Resolution
•
•
•
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Basic heuristics [Bilir 05] & [Xin 06]
Graph minimization approach [Yao 03]
ISOMAP based dimensionality reduction approach [Xin 06]
Graph based induction
Internet Topology Discovery
30
Anonymous Router Resolution
Problem

Anonymous routers do not respond to traceroute
probes and appear as a  in path traces
• Same router may appear as a  in multiple traces.
• Anonymous nodes belonging to the same router should be resolved.
U
S
y

H
L
x
Anonymity Types
1.
2.
3.
4.
5.
K
Ignore all ICMP packets
ICMP rate-limiting
Ignore ICMP when congested
Filter ICMP at border
Private IP address
S
y
z
W
A
Sampled network
C
U
z
W
L
Internet Topology Discovery
N
C
x
A
Resulting network
31
Issues in Topology Construction - III
at Router Level

Genuine Subnet Resolution
•
Inferring Subnets in Router-level Topology Collection Studies
[Gunes 07]
Internet Topology Discovery
32
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)
33
Summary

Introduction
•
•

Internet Topology Collection
•
•
•

Internet as a Complex Network
Motivations on Internet Topology Measurement
Basic Techniques
Some Measurement Projects & Platforms
Issues in Topology Collection
Issues in Topology Construction
•
•
•
Resolving Anonymous Routers
Resolving Alias IP Addresses
Resolving Genuine Subnets
Internet Topology Discovery
34
Questions ?
Internet Topology Discovery
35