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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. Roger Bacon 330 Roger Bacon 306 Mr. Swarner’s Office Network cables packed together in bundles; inside the ceiling and walls Turing Domain Controller DNS Server File Server
Internet
Campus DNS Server/Network Bridge Somewhere in Hines Hall Other Routers throughout campus Internet Connection Time Warner Business Class Network jacks where you can plug computers into the network Network Closet Routers installed on a rack
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.
- 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
- Ares – Compaq (Pentium III)
- Web Server
- 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.
- It made sure your login name and password were valid ( Domain Controller )
- It mapped a network drive so that you can store your data on Turing ( File Server )
- It tells your computer how to find other computers on the Internet ( DNS Server )
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? 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 Router
DNS
Server 168.0.
- Siena’s main DNS Server in Hines Hall then directs your data packet out to the Internet via our service provider Time Warner.
- Time Warner has a DNS Server that probably knows the IP Address of many URL’s.
- After several more hops, your data packet is routed to RPI’s Internet Service Provider, which knows what local netw ork www.rpi.edu is located on.
- 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).
- 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.
- The web page is then sent as a data packet and directed to your IP address. Meanwhile, your computer is awaiting this reply.
- 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.
