Aoraki Digital Technologies/Level 2/DT 2.50 AS91377/Explaining Simple IP Addresses

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Outline

The Internet Protocol is a set of rules for sending information between computers on the Internet. Each computer that uses the Internet Protocol has at least one IP address that identifies it to all other devices on the planet, just like a person might have a postal address.

This set of rules is like a language, but in computer science it is a protocol. A board of engineers has defined some of those protocols, which sit on top of each other (that's called layered architecture). On top of the Internet protocol there is the Transmission Control Protocol and the User Datagram Protocol (and some others). Below it, there are protocols of the Network layer, like Ethernet.

At the moment there are two versions of the Internet Protocol being used. One is called IP Version 4 (IPv4), the other one is called IP Version 6 (IPv6).

IP address

An IP address is a number given to each Computer on the Internet. It is like a postal Address or Telephone number, but for the computer. Internet protocol (IP) defines how communication from one address to another work.

Some computers have the same IP address for a very long time. These IP addresses are called "static IP addresses". Some computers change their IP from time to time. These IP addresses are called "dynamic IP addresses".

IP Version 4

With IPv4, each address consists of four numbers, called Octets. They go from 0 to 255. To make an IP address, one takes 4 such numbers. To translate between an IP address and the name of the computer, a system called Domain Name System is used. It can translate between the name and the IP Address.

An IPv4 address could look something like this

85.52.74.183


but an IPv4 address of 326.125.82.234 is not possible because one of the numbers is greater than 255.  

With IPv4, some addresses are reserved for special purposes. For example, 127.0.0.1 is the ip address the computer a user is working on looks at itself.

Activity - How are IP addresses given to computers?

Ping and Traceroute

  1. Using this online ping tool http://centralops.net/co/Ping.aspx find out the ip address of the following websites (ask your teacher if you are unsure about how to do this):
    • Slashdot.org
    • Metservice.co.nz
    • Google.com
  2. Using the following online utility, http://www.kcbbs.gen.nz/cgi-bin/trace trace some computer packets across the internet to the 3 websites above. Notice how the ip addresses of the intermediate computers (hops) follow the rules about ip addressing (ie no number is larger than 255).
  3. The worldwide scheme for giving out IP addresses is actually quite simple.  The ip addresses that can be used on LANs (ie they are not addresses on the internet) are as follows
Class ip address
A 10.0.0.0 through 10.255.255.255
B 172.16.0.0 through 172.31.255.255
C 192.168.0.0 through 192.168.255.255

Other ip addresses are "public" and used for computers or devices attached directly to the internet.  Check that the ip addresses discovered in the traceroute activity above do not fall into the private range. An international organisationICANN gives out ip addresses to Telecommunications companies (such as Telecom, Orcon etc) who in turn give them out to customers.

Public or Private?

Are the following ip addresses public or private?

  • 202.21.128.102
  • 210.55.11.13
  • 10.156.27.82
  • 50.30.33.78
  • 11.126.65.231
  • 192.168.10.3

Which could be used for a device directly connected to the internet?

Static or Dynamic?

In our first activity we manually assigned the ip address to the computer by editing a setting.  The computer would always have the same IP address (10.168.11.5) so it is called a static ip address.  There is a way to get computers to automatically get an IP address using a protocol called DHCP.  

  • Using the network set up in activity one, add a router to the switch.  
  • Set the routers IP address to 192.168.20.1. Configure the router to give out ip addresses in the range 192.168.20.2 through to 192.168.20.10.  
  • On your zenix computers, change wicd so that "use Static IP's" is unticked.  
  • Using the sudo ifconfig command check the IP addresses of you computers.  Has dynamic addressing worked?
  • Can you ping the routers address?
  • What sort of situations require static addressing and which required dynamic addressing?

Explaining IP Addresses in Detail

Read the following summary of how ip addresses work and do the exercises at the bottom of the page.

http://en.wikibooks.org/wiki/A-level_Computing/AQA/Computer_Components,_The_Stored_Program_Concept_and_the_Internet/Structure_of_the_Internet/IP_addresses

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