DNS Exercises

DNS (Domain Name System) is a system that allows you to use 'friendly names' instead of IP addresses. Many applications use DNS for user convenience. PING and TRACEROUTE are in fact applications and CyberKit allow the use of these 'friendly names'. Also, CyberKit allows for using DNS as an application in its own right, the implementation of this application is known as NS LookUp. For the backgrounds of DNS, needed at this stage of the practical training, we refer to What is DNS?. In that document some basics are explained and a small example, showing how to derive the IP address given a 'friendly name' (or hostname).

Install CyberKit

To install CyberKit you have to download the cyber.zip file, unzip it and go through the setup procedure:

• If you are familiar with these steps, you can start installation by using this link.
• If you are NOT familiar with these steps, you can do it step- by-step using this instruction page.

Some Web Servers and their IP-addresses

(WWW-) Server	IP-address
Internet Engineering Task Force (IETF)	132.151.1.19
World Wide Web Consortium (W3C)	18.23.0.22
SURFnet	192.87.46.9
PTT-Telecom	145.7.233.125
Nederlandse Spoorwegen	195.108.47.18
VVV	62.12.26.23
Planet Internet	195.121.6.143
ANWB	212.136.107.254

Hostnames of some Web-Servers

In the previous exercises (PING and TRACEROUTE) you have used IP addresses to execute these applications. In this part you will exercise to find the associated hostnames.

When you have read the document What is DNS you already know that the hostname of the IETF Web Server is www.ietf.org.

Do the following yourself:

1. Select the 'NS LookUp'-tab of the CyberKit application,
2. Fill in one of the above IP addresses in the 'Host or Address'-field,
3. Set the 'Type of Search'-field to 'Use Winsock Function GetHostByX',
4. Set the 'Clear Output'-field on,
5. Set the 'Verbose Format'-field off,
6. Push the 'Go'-button.

• What is the hostname associated with the IP address that you selected?
• Is there an alias for the hostname?

Repeat this exercise for some more Web servers in the list above!

IP Addresses of some Hosts

You are already familiar with surfing The Web! In the 'Location'-field of your browser you see things like: http://wwwhome.cs.utwente.nl/~codi, this is called the URL (Uniform Resource Locator) which uniquely identifies any Web document in the Internet. The part between '//' and the first '/' is actually a hostname. With DNS you can find out what the IP address of the host is. This can be found out as follows, fill in the following:

1. Host or Address = wwwhome.cs.utwente.nl
2. Set the 'Type of Search'-field to 'Use Winsock Function GetHostByX',
3. Set the 'Clear Output'-field on,
4. Set the 'Verbose Format'-field off,
5. Push the 'Go'-button.

In the result window you will see the result returned by the DNS service.

Questions:

• What is the IP address of the host named wwwhome.cs.utwente.nl
• Is this the actual name or an alias.
• What is the actual name of the Web Server.

Find out what the IP address is of some of your personal favortite Web Sites.

Advanced use of DNS

Although it is outside the scope of this exercise, you can find out many more things about Internet Hosts using the DNS Service Provider. All you have to do is select different options in the 'Type of Search'-Field.
If you do this, you must fill a 'Name Server', a possible one is ns1.surfnet.nl

- End of DNS Exercises -