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Describe the roles that a computer can take in a networked world.


Teaching Note:

Roles include client, server, email server, DNS server, router and firewall.


Sample Question:

A small company has a LAN connecting its various desk-top computers and peripheral devices.

The company is going to provide Internet access to its LAN.

(a) State the name of an additional hardware device that would be required to permit
Internet access. [1 mark]

(b) Explain how a firewall would help to provide security for the LAN. [3 marks]

(c) Suggest, with reasons, two further measures that the company should take to
safeguard its data from unlawful access via the Internet. [4 marks]

JSR Notes

Firstly, note that all of IB CS Topic 3 is Networks, so there is lots more to follow later on. (JSR: So maybe wait before going over too much here. Or maybe not; just do this first spiral without too much detail, or time.)


The Client-Server model

In this model, computers/devices are linked together somehow to establish a network. And in this system/model, each device/computer is wither a client or a server to others.

Client - any computer/device which receives services from another computer/device.

Server - any computer/device which serves data and/or other resources to a client. Note that this does not have to be a dedicated, high powered device, though this is often the case; rather any device can act a server to serve other devices.


Examples of Servers

(These are the two mentioned in the Teaching Note; see below for a description of other common servers.)

E-mail Server - An e-mail server allows client computers/devices to set up new e-mail accounts, and will manage all of the sending and receiving of e-mail. E-mail servers are easy to set up, and there are a variety of program out there that can allow a computer to act as an e-mail server, as long as the user maintains a domain to which the e-mail can be associated. (So for example, I have a bunch of e-mail addresses I can use with my johnrayworth.info website, such as john@johnrayworth.info.)

DNS Server - A DNS server is a Domain Name Server. These are servers which help the Internet keep track of where to find all websites (...or at least all websites whose users want for them to be found). Each DNS server is fundamentally no more than a table of IP addresses and their associated Internet website names (URLs). So for example, the two DNS records for my website are:


If people could remember the IP addresses of all their websites they use, then that would work too, but obviously that would be a ridiculous approach. So, rather, whenever a particular domain URL is typed into a browser, the computer queries the nearest DNS server on the network, which, if it itself keeps a record of that particular domain, will report back immediately the IP address to use, and otherwise will keep on contacting other DNS servers until a matching record is found, and then that IP address is returned (all of which seems to happen instantaneously to the user).


Other Important Server Computers

Router - a device that routes a file or a other data from one place to another. A router can be as simple as the one that you have as part of your modem, which connects to the Internet and distributes the signal either in a wired or a wireless way to other devices in your house. Or a router can be one of a a more robust variety, which routes data to many more devices than that, as within an office building or school. Wireless routers, like the ones attached to the ceilings of our classrooms simply do this wirelessly.

Firewall - a special server or software application, which keeps a "white-list" of IP addresses that it will allow to access the computer or network that it is protecting. So it is similar to a DNS server in the way that it has a list of the IP addresses. A firewall can be as simple as the one that comes as part of a computer's operating system, or a lot more sophisticated.

The maintenance of the white-list of all current safe sites in the world is a time-consuming, continual, and complicated process, which is why good firewall services - like the ones that a school will lease - cost a lot of money. And you'll note that these firewall companies often supply dedicated hardware firewall servers, which come with the firewall services package.


Other School-related Examples of Servers

A - Around the School

Around a typical school, any and everything that can be shared is done within the context of a client-server model. Servers usually include:

B - Servers I have run myself over the years

In the past I have set up and managed a variety of my own servers that worked to serve my own content management system, one that worked similarly to Moodle/Haiku/Google Classroom. Some of these servers, I ran right on my own classroom computer, which had a dedicated (i.e. non-changing) IP address. And at other times, I ran them via racked servers, the hardware of which, the school maintained.



Again, remember to see Topic 3 of this syllabus as well, particularly related to this assessment statement, 3.1.



Jaime: server: sending and receiving?

League of Legends, Battle.net Starcraft etc. are all good examples of client-server with central server.

Minecraft and many Steam games you can host your own server.

Deep web and DNS - things not listed on public DNS servers ----??? www???

(not the Dark net....)


DNS Table: (http://media02.hongkiat.com/dns-propogation-check/ceipam.jpg)


Jose: Dedicated game servers have responsibilities to that gaming community - ridiculous to be taking a couple of minutes to change servers.