Notes On Chapter Two -- Motivation and Tools

• 2.1 Introduction
  
  
• 2.2 Resource Sharing:
  • e.g. share printers, share files, share powerful CPU's.
  • How does this relate to stories about how the Internet got started? Some stories claim that the original motivation was to get a network that would survive a nuclear attack. Comer claims that it was ARPA's desire to share powerful CPU's among scientists who needed to analyze large data sets.
  • ARPA put together a large group of the best and brightest individuals available and they created the Internet. The story has something of the flavor of the story of the Manhattan project.
  
  
  
• 2.3 Growth of the Internet
  • Log plots show that the number of hosts (computers) on the Internet has been doubling every 9-12 months since the early '80's.
  • What has been the relative growth in various areas of the world? 1997 Internet Penetration
  
  
  
• 2.4 Probing the Internet -- use of ping
  • Who keeps track of how big the Internet is getting, and how do they do that? Nowadays it is done using DNS queries, ping, and statistical sampling techniques. Check out details here: Internet Software Consortium
  • Everbody who troubleshoots Internet connections should know about ping. It is the first tool you use to see if you can reach a host from where you are. (Do a demo of ping.) Ping is basically just an echo-response test. You send a packet to a host, and it replies by sending a packet back to you.
  • Ping command: ping altair.csustan.com
  • Ping command: ping -s altair.csustan.com
  
  
  
• 2.5 Interpreting A Ping Response.
  • It can be hard to tell what is the reason for a failure. A link could be down, a host could be down, software on the host could have failed, software in the target network could be configured to refuse to reply to ping requests.
  • What is a scenario that illustrates the use of ping? If your local host is having troubles and you know which remote hosts it depends upon for services, you can ping all those remote servers to see which one(s) your local machine is having trouble reaching. This helps point you in the direction of what needs to be fixed.
  
  
  
• 2.6 Tracing A Route -- do a demo of use of the traceroute utility
  • When you send a packet from computer X across the Internet to computer Y, it usually travels through a series of other computers (routers) along the way. You can use traceroute to identify those intermediate computers.
  • Some of the routers may not respond to traceroute and therefore traceroute may not discover all of them.
  • Although routes tend to be pretty stable over short time spans, two packets sent from X to Y may travel different routes at different times. The information obtained from traceroute can be misleading.
  
  
  
• 2.7 Summary
  • Flavors of Unix include ping, traceroute and other network utilities in their system software distributions.
  • Personal computer users may not have these utilities "built-in." However, one can download software packages that include ping and traceroute, or one can get access to ping and traceroute servers on the world wide web. Search
  • Search TUCOWS for ping software.
  • If you want a web-base ping or traceroute server then look at this SLAC page.