Networks | Part 3 of 3
In Chapter 46 More on LANs we built on the basics of networking by looking at different configurations, topologies, protocols and media used. We also looked at wireless connections and discussed some examples of networks with different devices. For the last part of the series we will be speaking about addressing and take a closer look at some of the networking devices we use to configure a network.
We learnt that computer networks are built for the purpose of communicating and sharing resources. This means that data, which we refer to as packets, must travel from one device to another on the network. How does the network keep track of which device is which?
It turns out that the solution is much like how you would send a physical parcel to someone you care about...
Addressing
Addressing is a means by which a computer network can uniquely identify the devices connected to it. You guessed it devices on a network are assigned addresses. An address can take one of the two main forms: a MAC address or an IP address (you probably heard of this one).
MAC Address (Physical Address)
MAC stands for Media Access Control Address. A MAC address is a hardware identification number that uniquely identifies each device on a network. Most modern devices you buy come equipped with a NIC (Network Interface Controller) card (Ethernet card or Wi-Fi card) and the MAC address is manufactured into it. Since it comes directly from the manufacturer this cannot be changed!
There are millions of networkable devices in existence and each of them must have a unique MAC address. How can we ensure uniqueness? By having a very (very, very) wide range of possible addresses. In fact MAC addresses are made up of six two-digit hexadecimal numbers separated by colons. For example, an Ethernet card may have a MAC address of 00:0d:83:b1:c0:8e. Fortunately you do not need to know this address, since it is automatically recognised by most networks. Should you need to though you can find it.
IP Address (Logical Address)
An IP address, or simply an IP, is a unique address that identifies a device on the internet or a local network. There are two primary types of IP address formats used today — IPv4 (v means version) and IPv6. The key difference between the two is that IPv4 is a numerical address and IPv6 is alphanumerical so that it could support a much wider range of addresses. If you are interested you can read more here.
In summary, MAC Addresses and IP Addresses are both used to identify a computer on a network or on the internet. The MAC address is provided by the NIC's manufacturer and gives the physical address of a computer. Whilst the IP address is a logical address that is provided by an Internet Service Provider (ISP) when the computer needs to connect to the internet.
Networking Devices: Modems and Routers
Let's bring back the example of Simple Home LAN #3 depicted hereunder:
Apart from the computers and devices we interact with (desktops, laptops, tablets, phones, consoles and printers) there are also devices with which we don't really engage much. We are referring to the networking devices that make communication across the network and beyond possible. See if you can spot the following examples in the diagram.
Modems
Wireless Routers
Hubs or Switches
What is the difference between a modem and a router? This is a good question because nowadays these two are embedded into one device so it is very easy to use the terms interchangeably. Not too long ago we used to buy two separate devices as illustrated below because indeed each device has a specific purpose:
Your modem is a box that connects your home network to the wider Internet.
Your router is a box that lets all of your wired and wireless devices use the Internet. It also allows them to talk to one another without having to do so over the Internet.
As we mentioned earlier your ISP will give you one box that serves as both modem and router, but they’re still different technologies; not all modems include routers and not all routers have modems. You need both, integrated or not, in order to provide an Internet connection for all the devices in your home.
How Does a Modem Work?
A modem modulates and demodulates electrical signals sent through phone lines, coaxial cables, or other types of wiring; in other words, it transforms digital information from your computer into analog signals that can transmit over wires, and it can translate incoming analog signals back into digital data that your computer can understand.
Most standalone modems have just two ports: one that connects to the outside world, and an Ethernet jack that connects to a computer or a router.
A common attribute of a modem is the download and upload speeds, which determine how fast data comes into and out of your home. These make a big difference when performing bandwidth-heavy actions like...
Watching Netflix (needs fast download speed)
Gaming (needs fast download and upload speed)
Downloading software (needs fast download speed)
Many types of modems are available and the distinction is normally in the physical infrastructure being used and the load it can sustain. We list a few examples hereunder.
DSL Modems
DSL refers to Digital Subscriber Lines, ADSL (common in homes) is a type of DSL.
Able to transmit a signal via a copper phone lines at speeds over 100 Mbps. In practice however it tends to be around 7 to 25 Mbps.
Enables users to talk on the phone while simultaneously accessing the internet.
Cable Modem
Operates over cable tv lines i.e. coaxial cables which incidentally provide greater bandwidth than telephone lines.
Most providers offer service between 1 Mbps and 16 Mbps bandwidth for downloads, and up to a few Megabits for uploads.
Users are always connected to the internet.
Fiber Optic Modem [Most Popular]
The medium of transmission is glass and data is carried in beams of light.
Fiber internet is not affected by deteriorating copper phone lines or hindered by crowded cable lines therefore it can transmit more data farther and faster!
Fiber gives users the best experience.
Wireless Modem
Data travels via electromagnetic wave transmission.
Very suitable for smartphones due to lack of wiring and convenient size.
Several wireless technologies on the market at the moment e.g. Bluetooth (via UHF radio waves), Wi-Fi and WiMAX (via microwaves).
How Does a Router Work?
Your router’s primary responsibility is to route data between devices in your home, and between those devices and the wider Internet. The system of interconnected devices plus the router itself is what we’re collectively referring to when we talk about a home network. Your modem connects to one port on the router — usually (but not always) labeled “Wide Area Network”, “WAN”, or "Internet" — and all of your devices connect to the other ports, or wirelessly over the Wi-Fi standard.
Routers have a routing table in it that is refreshed periodically according to the changes in the network. To transmit data packets, it consults the routing table. To prepare or refresh the routing table, routers share information among each other.
Virtual Private Networks (VPN)
A Virtual Private Network (VPN) is a way to securely connect two or more devices over the internet. VPNs are like a secret tunnel that allows information to travel from one device to another without anyone else being able to see it.
VPNs can be used in two different ways:
Site-to-Site VPN
This is like a secret tunnel between two networks, such as two different school buildings. For example, if your school has two campuses and you want to share information between them, you could use a VPN to create a secure connection between the two networks. This way, you and your classmates could access resources on the other campus without anyone else being able to see what you're doing.
Remote Access VPN
This is like a secret tunnel between a device and a network, such as your laptop and your school's network. For example, if you are working on a project from home and need to access resources that are only available on your school's network, you could use a VPN to securely connect to the network. This way, you could access the resources you need without anyone else being able to see what you're doing.
Play and Learn
Play a network simulator game to see how data travels within a computer network, with an emphasis on security (🔥hot exam topic). As you progress in the game you will also learn how to perform attacks using techniques that real hackers use!
What does a modem do? A modem connects your home network to the wider Internet.
What does a router do? A router routes data between devices on the same local network and routes data between devices over an internet connection.
What uniquely identifies a device on a network? Devices on a network can be uniquely identified using addresses. Every device comes with a unique MAC (physical) address assigned by its manufacturer. A device that is connected to the internet is assigned a unique IP (logical) address.
What is a Virtual Private Network (VPN) and how does it work? A VPN is a way to securely connect two or more devices over the internet by creating a secret tunnel that allows information to travel from one device to another without anyone else being able to see it.
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