Download Lab 1 – The Basics - Computer Science

Lab 1 – The Basics
Introduction - The Computer Science Department at Siena College is a model computer network. It is
very similar to networks that you may encounter in your professional life. Thus, I think its important to
study it so that you understand the setup of a modern computer network.
Turing
 Domain Controller
 DNS Server
 File Server
Roger Bacon 330
Mr. Swarner’s
Office
Network jacks
where you can
plug computers
into the network
Routers
installed on a
rack
Network
Closet
Network cables
packed together in bundles;
inside the ceiling and walls
Other Routers
throughout
campus
Internet
Internet Connection
Time Warner
Business Class
Campus DNS Server/Network Bridge
Somewhere in Hines Hall
Roger Bacon 306
Client/Server Concepts
Right now, you are on a client computer. Specifically, you are on a PC (personal computer). PC
indicates that the computer is used by one person at a time.
Right now, I hope that nobody else is using the processor or hardware on your computer.
Discussion Question: In certain situations, it is possible for a PC to be simultaneously used by
more than one person. In fact, it is possible that you could setup the PC in front of you so that
hundreds of people could use the processor or hard drive. Can you think of such a scenario?
When you login, your client computer contacts a server. Specifically, you contact a computer called
Turing, which is located in Ken Swarner’s office.
Unlike a PC, a server is used by multiple users. Servers are typically more powerful than PC’s, but that
is not always the case.
The CS Dept. has three different servers that you should know about.
1. Turing - Dell (Dual Xeon)
 Domain Controller – controls who can login to the CS Network
 File Server – stores and retrieves files in your Home Directory
 Domain Name System (DNS) Server
2. Ares – Compaq (Pentium III)
1. Web Server
3. Oraserv – Dell (Pentium III)
 Database Server
Discussion Question: Your computer is actually much more powerful than our Web Server. Our
Web Server is just a normal Pentium III PC; How can we really classify it as a server? What
really defines a server?
When you logged-in today, Turing did 3 things.
1. It made sure your login name and password were valid (Domain Controller)
2. It mapped a network drive so that you can store your data on Turing (File Server)
3. It tells your computer how to find other computers on the Internet (DNS Server)
Home Directories
You have an account on the Computer Science Department's network.. Part of your account includes a
Home Directory on the department's file server (Turing).
A Home Directory is simply a folder on the file server where YOU can store your files. Every student in
the department has a home directory.
File Server Details:
For your information, Turing is a Dell PowerEdge2650 Dual Xeon Processor Server. It has 2.4
Gigabytes of memory (RAM) and it has 1.5 Terabytes of disk storage. By the way, 1.5 Terabytes equals
1500 Gigabytes.
Turing actually has about 10 hard drives and each hard drive can store about 150 Gigabytes of data.
Turing needs a lot of disk storage because a lot of people have Home Directories.
In a given year, there are almost 1000 different students who take computer science courses. Thus, there
are nearly 1000 Home Directories stored on Turing's 10 hard drives.
Turing
Hard Drive 10
Hard Drive 1
user1
user2
user3
user997
user998
user999
Discussion Question: What is the main advantage of having a file server? Why not just store your
files on the PC’s hard drive?
Task 1:
1.
2.
3.
4.
5.
Find the My Computer Icon on your computer
Click on it
Try to find your mapped drive.
Open it.
What is the capacity of the hard drive? __________________
6. How much free space is available? ___________________
7. Check with two other people in the class to see if your answer match.
8. Do your answers match? Yes or No
Network Concepts
In order to route data on the Internet, computers are assigned addresses called IP Addresses (IP stands
for Internet Protocol).
An IP Address has four numbers separated by decimal points.
The computer you are using today, has the following IP Address:
192.168.0.x
where




192 tells that you are at Siena College,
168 indicates that you are on the CS Dept. Network,
0 specifies that you are on the primary sub-network, and
x indicates your specific computer.
Note: Each number can range from 0 to 255. Thus, if the CS Dept. had more than 256 computers we
would need to have more than 1 sub-network.
A Router directs data packets to multiple cables. A Router also has a small processor and some
memory. It tries to route data packets to the correct cable. Thus, Routers have information about each
computer attached to the network..
Discussion Question : Does anyone know how older networks were setup?
DNS
Server
168.0.1
168.0.2
168.0.3
168.0.4
Router
Internet
168.0.2
Each data packet includes the IP address of the computer where the packet is going. The router should
know the cable where each computer is connected.
On our network, a computer is not truly recognized until it is assigned an IP address by the system
administrator. The system administrator does this by updating a table on the DNS Server and/or a table
directly on the Router.
If the system administrator has to update this table manually, the network uses what is called Static IP
Addresses.
Discussion Question : What are some of the disadvantages of a network that uses Static IP
Addresses? Can you think of a better way to set up a network?
Internet Routing
Task 2
1. Open up a web browser and go to www.rpi.edu.
Note: This web page was sent from a web server somewhere on RPI’s campus to your
computer.
Discussion Points:
How did your computer know where to find the web server?
How did the web server know where to find your computer?
2. Find a program called Putty.
3. Click on it and open it
4. Type turing where it asks for the host name
5. Login using your user name and password
6. At the command prompt, type the command: traceroute www.rpi.edu
7. Wait for the results to finish displaying
8. How many “hops” did it take to go from Siena to RPI? _____________
How things work (please read):
1. The system administrator configured your computer so that your computer knows the IP Address
of the local DNS Server.
2. Your web browser initiates a request to find www.rpi.edu. This request is sent to the local DNS
Server. This request is just a packet of data directed to www.rpi.edu.
In general, DNS Servers have tables where they can look up a URL like www.rpi.edu to find the
IP Address of that URL.
3. In this case, our DNS Server (Turing) could not find www.rpi.edu on the local network. Thus,
Turing directs your packet of data to an external DNS Server (probably located in Hines Hall).
In general, every new DNS Server has to piggy-back off of an existing DNS Server. This is how
information is shared with new networks. Our DNS Server piggy-backed off of Siena’s main
DNS server, which piggy-backed off some other DNS server.
4. Siena’s main DNS Server in Hines Hall then directs your data packet out to the Internet via our
service provider Time Warner.
5. Time Warner has a DNS Server that probably knows the IP Address of many URL’s.
6. After several more hops, your data packet is routed to RPI’s Internet Service Provider, which
knows what local network www.rpi.edu is located on.
7. Eventually, your data packet is transmitted on the correct local network and directed via a router
to www.rpi.edu, which is actually a computer (a web server).
8. RPI’s web server interprets your data packet and realizes that it’s a request for a web page. The
request includes the IP address of your computer.
9. The web page is then sent as a data packet and directed to your IP address. Meanwhile, your
computer is awaiting this reply.
10. Given that all the network connects are fast, this whole process can take less than 1 second.
Final Notes:
Putty is a program that allows you to directly connect to servers. In this case, we directly connected to
Turing, which is our file server, domain controller, and DNS server.
Turing has a command-line operating system called Linux, where you can directly type commands.
traceroute is a command that reports the routing information for a specific URL.
A URL is a Uniform Resource Locator. You can think of it as a human readable IP Address. URL are
translated into numeric IP Addresses by DNS Servers. Later in the semester, we will talk about how to
obtain URLs and how this has turned into a very important business.
Linux is a very reliable operating system (unlike Windows which often crashes). Linux is primarily a
command-line operating system, which means that it doesn’t have a pretty user interface like Windows.
Basically, all you get is text area where you can type commands. However, if you logged in directly on
the server, you would have access to a Windows-like interface for managing the server.