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. 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

Flow chart of our diagnostic tool

Local Network Settings

DNS Related problem

Diagnosing Remote HTTP Host

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

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

Sections from the Look-up table

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)

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

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

A Snapshot of our system