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A tool for diagnosing internet connectivity problems

A tool for diagnosing internet connectivity problems. Presentation by: Masaharu Kobashi Rosalia Tungaraza Computer Networks, Autumn 2004. What could have gone wrong when you can’t access a web server?. Our Goals: Build an integrated system that diagnoses the above problem.

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A tool for diagnosing internet connectivity problems

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  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 0 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. 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 • 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

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