[GCC-Study] Networking (1)

1. What is networking

Basics of Networking

When most people think of the Internet, they think of a magical cloud that lets you access your favorite websites, shop online, and you're seemingly endless stream of cat pictures. But there isn't any magic involved. There's no mysterious entity that grants us a cat picture on demand. The Internet is just an interconnection of computers around the world, like a giant spider web that brings all of us together. We call the interconnection of computers a network. Computers in a network can talk to each other and send data to one another. You can create a simple network with just two computers. In fact, you might already have your own network at home connecting all of your home devices. Let's think on a bigger scale. What about the computers at your school or workplace? Are they in a network? They sure are. All of the computers there are linked together in a network. Can we link your home, school and workplace networks together? We absolutely can. Your workplace connects to a bigger network, and that network connects to an even bigger network, and on and on. Eventually, you've got billions of computers that are interconnected, making up what we call the Internet. 

 

You, like most people, probably access the Internet through a browser, like Mozilla Firefox, Google Chrome, Microsoft Edge or something else. This is done through the World Wide Web. But don't make the mistake of thinking the Internet is the World Wide Web. The Internet is the physical connection of computers and wires around the world. The Web is the information on the Internet. We use it to access the Internet through a link like http://www.google.com. The World Wide Web isn't the only way we can access the Internet. Your e-mail, chat, and file-sharing programs are also ways you can access the Internet.

 

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In the IT field, managing, building and designing networks is known as networking. If you work in the IT field, it's super critical that you understand the fundamentals of networking. So how does it all work? The Internet is composed of a massive network of satellites, cellular networks, and physical cables buried beneath the ground. We don't actually connect to the Internet directly. Instead, computers called servers connect directly to the Internet. Servers store the websites that we use, like Wikipedia, Google, Reddit, and BBC. These websites serve content. The machines that we use, like our mobile phones, laptops, video game, consoles and more, are called clients. Clients request the content, like pictures, websites, from the servers. Clients don't connect directly to the Internet. Instead, they connect to a network run by an Internet service provider or ISP, like CenturyLink, Level 3, Comcast, Telefonica, and things like that. ISPs have already built networks and run all the necessary physical cabling that connects millions of computers together in one network. They also connect to other networks and other ISPs. These other networks connect to the networks of Google, Reddit, and universities.

 

Basically, all the other networks in the world, together, they form one giant network of computers called the Internet. But how do the clients know how to get to servers? Well, how would you send a letter to someone? You'd put your address on the letter and send it to the address of the person you're sending the letter to. Computers have addresses just like houses. Computers on a network have an identifier called an IP address. An IP address is composed of digits and numbers like 100.1.4.3. When we want to access a website like http://www.coursera.com, we're actually going to their IP address like 172.217.6.46. Devices that can connect to a network have another unique identifier called a MAC address. MAC addresses are generally permanent and hard-coded onto a device. A sample MAC address can be something like this.

 

MAC address

 

When you send or receive data through a network, you need to have both an IP and a MAC address. You might be wondering why we need to have two different numbers to identify something. That's a good question. Think again of the letter analogy we used before. An IP address is your house address, while the MAC address is the name of this recipient of the letter. He want to make sure your letter gets to the right location and to the right person. A more simplified example of the letter delivery would go like this. I'm in New York City, and I got a letter that I want to send to a friend, Mey. Mey is halfway across the world in Tokyo. So our letter will go through lots of places before it reaches her. I put her name and address on there, and I also put my name and address on there too. When I drop my letter off at the post office, the mail person looks at it. He thinks, "I don't know how to get to Tokyo from here, but there is a truck that's headed to Texas." He puts my letter in that truck. At the post office in Texas, a mail person looks at the letter and says, "I don't know how to get to Tokyo from here, but we have a truck going to San Francisco." She puts my letter in that truck. At the post office in San Francisco, yet another mail person looks at my letter. He says, "Oh, there's a plane headed to Tokyo." And puts the letter on that plane. When it finally reaches Tokyo, the postman there says, "Oh, I know where Mey lives," and delivers the letter to her. Obviously, there are many more nuance to mail delivery than what I described, but this process is similar to how information gets routed across the Internet. One thing to call out is that data that is sent through a network is sent through packets. There are little bits of data, and you guessed it, ones and zeros. It doesn't matter if it's pictures, email, music, or text. When we move data through the network, we break them down into packets. When a packet gets to its destination, it will rearrange itself back in order. Think of a packet like a letter. Let's actually look at this process again, but this time, we'll use IP addresses and MAC addresses. Natalie has a computer with IP address 113.8.81.2, and she wants to go to google.com and search for pictures of cats. Before she does that, her computer has to send a packet to ask google.com if it can access their website. Our packet knows google.com's IP address is 172.217.6.46, but it doesn't know how to get there just yet. The packet travels from one place to another at each destination, where it asks, "Hey, do you know where google.com is?" Eventually, it will be routed to another destination that can get the packet closer and closer to google.com. Once it reaches a destination that can deliver the packet to a server at google.com, Google will send Natalie a packet saying she can access an unlimited number of cat pictures. 

 

 

Networking Hardware

Now that we understand what networks are, let's talk about how they're connected. There are a lot of ways you can connect computers to a network. First, there is an Ethernet cable, which lets you physically connect to the network through a cable. On the back of the desktop we worked in the previous lessons, there's a network port that you plug your Ethernet cable into. Another way to connect to a network is through Wi-Fi, which is wireless networking. Most modern computing systems have wireless capabilities like mobile phones, smart televisions and laptops. We connect to wireless networks through radios and antennas. The last method will go over uses fiber optic cables to connect to a network. This is the most expensive method since fiber optic cables allow greater speeds than all the other methods. Fiber optic gets its name, because the cables contain glass fibers that move data through light instead of electricity. This means that we send ones and zeros through a beam of light instead of an electrical current, through a copper wire.

 

 

But our cables have to connect to something. We don't just have millions of cables going in and out of computers to connect them together, instead, computers connect to a few different devices that help organize our network together. The first device that your computer connects to is a router. A router connects lots of different devices together and helps route network traffic. Let's say we have four computers, A, B, C and D, connected together through a router in the same network. You want to send a file from Computer A to Computer B. Our packets go through the router and the router utilizes network protocols, to help determine where to send the packet. For now, just know that our router uses a set of rules to figure out where to send our data.

 

So, now our packet gets routed from Computer A to Computer B. What if you wanted to send a packet to a computer not in our network? What if we wanted to send a packet to our friend Alejandro's computer. Alejandro is on a different network altogether. Fortunately, our router knows how to handle that too. The packet will get routed outsider network to our ISP's network. Using networking protocols, it's able to figure out where Alejandro's computer is. During this process, our packet is traveling across many different routers switches and hubs. Switches and hubs are also devices that help our data travel. Think of switches like mailrooms in a building. Routers get our letters to the building. But once we're inside, we use the mailroom to figure out where to send a letter. Hubs are like company memos. They don't know who to send the memo to, so they send it to everyone. Working with network devices is important to understand, because it's likely that one day you'll have users reporting problems accessing the Internet. You want to investigate your way up the network stack. A technologies stack, in this case a network stack is just a set of hardware or software that provides the infrastructure for a computer. So, the networks stack is all the components that makes up computer networking. You might need to investigate the networks stack and your job. You'd start with making sure the end user computers are working properly. Then you'd turn your attention to other possible points of failure like the cabling, switches and routers, that work together to access the Internet.

 

Language of the Internet

We talked briefly about the networking protocols our devices use to help our packets get from one destination to another destination, but what are they? There are lots and lots of network protocols used and they're all necessary to help us get our packets in the right place. Think of network protocols like a set of rules for how we transfer data in a network. Imagine if you sent a letter to your friend Sasha who lives in California, but your post office sends it out to another Sasha who lives out in New York. That would hopefully never happen, since the post office has rules that they follow to make sure your letter is sent to the correct address. Our networking protocols do the same thing. There are rules that make sure our packets are routed efficiently, aren't corrupted, are secure, go to the right machine and are named appropriately. You get the idea. 

 

We'll cover specific network protocols later on, but there are two protocols that you need to know. The Transmission Control Protocol and the Internet Protocol, or TCP/IP for short, which have become the predominant protocols of the Internet. The Internet Protocol or IP, is responsible for delivering our packets to the right computers. Remember those addresses that computers use to find something on a network? They're called IP addresses or Internet protocol addresses. The Internet Protocol helps us route information. The Transmission Control Protocol or TCP, is a protocol that handles reliable delivery of information from one network to another. This protocol was an important part of the creation of the internet since it let us share information with other computers. We'll spend a lot of time diving into these protocols in the next course, the bits and bytes of computer networking, so stay tuned.

 

 

The Web

There are lots of different ways to use the Internet, we all know that. But I want to cover one of the more prevalent ways that people access the Internet, through the Web. All websites can be accessed through the Web. Websites are basically text documents that we format with HTML, or hypertext markup language. It's a coding language used by web browsers. Web pages are generally made up of very basic components. They contain multimedia content like text, images, audio and video. When you want to navigate to a website, you would type in a URL like http://www.reddit.com. 

 

A URL, which stands for Uniform Resource Locator, is just a web address similar to a home address. Notice the www in the URL? It stands for World Wide Web. The second portion, reddit.com, is something we call a domain name. Anyone can register a domain name. It's just our website name. Once a name is taken, it'll be registered to ICANN, the Internet Corporation for Assigned Names and Numbers. Once a domain name is registered with ICANN, no one else can take that name unless it becomes available again. The last part of the URL in this case is .com. But you can also use different domain endings like reddit.net or reddit.org. The different domain name endings are standards for what type of website it might be. So a domain that ends in .edu is mainly used for educational institutions. 

 

Remember how computers use IP addresses to find another computer? Well, you can do the same if you wanted to find a computer on the Internet. Let's go ahead and type 172.217.6.46 into a web browser and hit Enter. Wait a minute. What happened? How come we're at Google's homepage? It turns out the IP address, 172.217.6.46 maps to Google's homepage through a critical web protocol, Domain Name System, or DNS. DNS acts like our Internet's directory and lets us use human readable words to map to an IP address. The computer doesn't know what google.com is. It only knows how to get to an IP address. With DNS, it's able to map Google's IP address with google.com. Every time you go on a website, your computer is performing a DNS lookup to find the IP address of the website name you typed in. This trick can be a good first step in diagnosing certain kinds of DNS issues. So if you're able to access a website by its IP address but not its human readable domain name, then there's a good bet that there's probably a problem somewhere in the DNS configuration your network is using. Understanding IP addresses can come in handy in all sorts of other situations you might encounter as an IT support specialist. The source of Internet requests are usually identified by IP addresses and server logs. Many pieces of IT infrastructure need to have some kind of IP address configuration applied to them in order to work. DNS is a huge system, and we'll be discussing more about it later.

 

 

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