Text Version

Introduction

This lesson goes more deeply into the infrastructure and mechanics of the Internet. It explains packet switching, TCP/IP and the protocol hierarchy, as well as IP addresses and domain names.

(Slides)

How the Internet Works, Part 1

Activity 1 - Using Ping to Test the Reachability of Internet Hosts

The CentralOps.net has free interactive tools that can be used to observe packet routing, latency time, and other Internet statistics. Just choose the tool you want to use from the navigation bar on the left.

Ping tests whether a host computer is reachable by repeatedly sending data packets from the CentralOps.net server in Dallas, TX to the host computer.

• For each of the following servers, write down the average round trip time (RTT): google.com, yahoo.com, www.trincoll.edu, appinventor.mit.edu.
• Some questions to discuss:
  • Did any of the servers lose packets?
  • Are you able to find a server that has a really long RTT or does lose packets?

Activity 2 - Using Traceroute to Observe How Packets are Routed

Traceroute lets you trace the route from the CentralOps.net server in Dallas, TX to some destination server.

• Use Traceroute to identify the IP addresses and trace the routes to the following host computers: google.com, yahoo.com, www.trincoll.edu, appinventor.mit.edu.
• Use the Monitis Traceroute tool to measure the average latency between various servers on the Internet. How much time and how many hops do the following routes take:
  1. http://google.com
  2. http://whitehouse.gov
  3. http://mobile-csp.org

How the Internet Works, Part 2

Activity 3 - Packet Sniffers & Public Networks

Watch this video that describes how a hacker could view your data on a public network using a packet sniffer. Discuss with your classmates when and where you use public networks, how you use the Internet on them, and how you might protect your data.

How the Internet Works, Part 3

Activity 4 - Lookup Domain Names & IP Addresses

Using the tools below, try looking up the IP addresses for various websites, including their subdomains. Do you see any patterns? Now look up your school's domain name and IP address, and then the IP address for your computer or mobile device. Do you see any patterns?

• WhoIs.com - find the IP address for a given host name
• WhatIP.com - find the IP address of the device visiting the website
• What's my IP? - mobile version
• Possible searches: 1) google.com, maps.google.com; 2) www.wikipedia.org, en.wikipedia.org; 3) mit.edu, appinventor.mit.edu

Self-Check

Here is a table of some of the technical terms discussed in this lesson. Hover over the terms to review the definitions.

hôte routeur adresse IP nom de domaine ping traceroute

commutation de paquets paquet sniffeur de paquets couche d'abstraction

Sample AP CSP Exam Question

Still Curious

There is a wealth of good introductory and comprehensive information about the Internet and the WWW.

• As always, Wikipedia is an excellent resource as a first stop. Its pages on Internet protocol, Ping, Traceroute, and the other topics in this lesson are all accurate and accessible.
• The How Stuff Works site has a nice animated description of how routers work to direct traffic on the Internet.
• For a very detailed and comprehensive discussion of networking -- sort of like reading a short book -- see the CTDP's Networking Tutorial, which covers the topic in much more detail than we have done here.
• Explore this interactive map of the underwater cables that carry 99% of international data.