Tell me about SSL, VPNs and ports

VPN
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What is the source of network data?

In theepicsnail’s metaphor, the source is the mailman or or whoever gives the letters out to the kids. For your computer, the source is the piece of software - which is probably a part of your operating system - which listens to the incoming network traffic from your network cable connected to the computer, or the WiFi adapter that allows you to connect to the wireless network.

What are packets?

Packets are chunks of information. In theepicsnail’s metaphor, packets are the letters delivered to the kids at camp. Each packet has an address associated with it so everyone who works on delivering it knows where to make it go. As theepicsnail said, as well as an address, each packet also includes a number (the port), so that people who are in charge at that address can decide what to do with it once it has arrived.

What’s an FTP?

FTP stands for File Transfer Protocol. A “protocol” is a way of reading many packets together, so that they do something useful. In the case of “File Transfer Protocol”, the “something useful” is the ability to download and upload files. Another protocol is HTTP - you can read all about that here. To continue theepicsnail’s metaphor, imagine the camp leaders say parents can only send 1 sheet of paper per letter, but your mum wants to send you a big picture. It’s so big, it won’t fit in on one sheet, so she sends it as lots of letters, with a bit of the picture on each one. But for you to build the whole picture, you need to know whether to put all the letters next to each other (so that it’s a really long picture 1 sheet high), or whether you should make many rows and columns (and if so how many rows and how many columns). That knowledge of how to interpret all the letters together is a protocol.

I get the idea that ports are supposed to be used to direct data to different locations right?

Yes, that’s a good way of putting it. Specifically, it’s to help the operating system’s network layer decide which program should receive the data in a given packet. You might want to read/ask about MAC addresses and IP addresses, which are also used to direct data, but are quite separate from each other and from ports. It’s good to understand how they are different.

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Mostly to connect to the private internal network (intranet) of your workplace/university/school from oustide without making said network open to the public (and keep the transferred data secret/encrypted).

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Basically yea, they’re generally used for pirating nowadays. Reason is because ISPs (internet service providers, like Comcast, or Bell) can tell if you’re torrenting or not. Sometimes companies plant small viruses inside pirated movies so they can track who downloads it. With a VPN, you don’t have to worry about being caught.

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most commonly, you’ll find VPN being used in the enterprise/gov’t space for employees/agents to use in order to access network resources e.g. an e-mail server, intranet, shared storage, etc. that are located on another network than the user. Example, I’m a salesperson for company X on a business trip. I’m staying in a hotel and I need to access the e-mail server housed inside of my company’s headquarters 3000 miles away. I have a secureID token (one common VPN authentication tool) that generates a code matching a code at the destination office. I use that code to create a Virtual Private Network connection to that server. At this point, I can now access those resources as if I were plugged into the ethernet port at my desk back home. Boom.