1. A tool for diagnosing internet connectivity problems
Presentation by:
Masaharu Kobashi
Rosalia Tungaraza
Computer Networks,
Autumn 2004

2. What could have gone wrong when you can’t access a web server?
Our Goals:
Build an integrated system that diagnoses the above problem.
Make it easy to use and informative for users.
Learn about various network tools
Gain some experience in probing the internet for different information.
Why such a tool ?
Existing tools are not integrated (many functionalities required)
Some are too difficult to use for the average user

3. Flow chart of our diagnostic tool

4. Local Network Settings

5. DNS Related problem

6. Diagnosing Remote HTTP Host

7. Diagnosing remote host availability: Look-up table
Server’s past availability trend
infer
Server’s present availability
Hence, a look-up table
Contains all web servers that are actively listening for requests within a specific region
For each server there should be information gathered over a specific period of time about
Relative availability
RTT based on a specific source host

8. Collection of data MHC Massachussetts UW Washington Total IP addresses
65025
195075
Total IP addresses with domain names
12675
70094
Randomly selected 15% from above nodes
10305
Total IP addresses with servers on port 80 listening for requests
149
556

9. Sections from the Look-up table

10. Pathneck Bottleneck locator developed by a CMU group Strengths:
Light-weight and fast
Does not require cooperation by destination
Weaknesses
Cannot probe through firewalls having restrictions on the size of UDP packets
Cannot separate forward path problems from backward path problems (common weaknesses of all one-end mode tools)

11. traceroute / tcptraceroute
Summary of tools used
ifconfig
route
netstat
Local Network Settings
dig
(nslookup, host)
DNS
traceroute / tcptraceroute
ping
tcpdump
Remote Host
Path
Pathneck

12. What we learned Tools Obstacles to probing (Reality of the Internet)
Used 7 tools as components of our system
Impressive tools: tcpdump (pcap library), dig
Most path probing tools not appropriate for real-time diagnosis in single end mode (pathchar, pipechar, pathrate, pchar, nettimer, etc.)
Obstacles to probing (Reality of the Internet)
ICMP, UDP packets of ping, traceroute filtered or given lesser privilage at hops/hosts
Constantly changing IP – name binding at some sites
(e.g. yahoo)
Difficulties of system building
Root privilege (solved by “sudo”)
I/O synthesizing with component tools

13. A Snapshot of our system