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UDP. I'd make a joke about it, but I'm not sure you'd get it.

This episode is sponsored by ThousandEyes. Think of ThousandEyes as the Google Maps of the internet. Just like you wouldn't dare leave San Jose to drive to San Francisco without checking if 101 or 280 was faster and yes, that's a very localized reference to San Francisco Bay area. Businesses rely on ThousandEyes to see the end to end paths their apps and services are taking from their servers to their end users to identify where the slowdowns are, where the pileups are hiding and what's causing the issues. They use ThousandEyes to see what's breaking where and importantly, they share that data directly with the offending service providers to hold them accountable and get them to fix the issue fast, ideally before it impacts end users. You'll be hearing a fair bit more about ThousandEyes over the next 12 weeks because Thursdays are now devoted to networking in the cloud. It's like screaming in the cloud, only far angrier.

We begin today with the first of 12 episodes. Episode one, the fundamentals of cloud networking. You can consider this the AWS morning brief networking edition. So a common perception in the world of cloud today is that networking doesn't matter, and that perception is largely accurate. You don't have to be a network engineer the way that any reasonable systems or operations person did even 10 years ago, because in the cloud, the network doesn't matter at all until suddenly it does at the worst possible time, and then everyone's left scratching their heads.

So let's begin with how networking works, because a computer in 2019 is pretty useless if it can't talk to other computers somehow. And for better or worse, Bluetooth isn't really enough to get the job done. Computers talk to one another over networks, basically by having a unique identifier. Generally, we call those IP addresses here in the path that this future has taken. In a different world, we would've gone with token ring and a whole bunch of other addressing protocols, but we didn't. Instead we went with IP, the unimaginatively named internet protocol, and with the current version of the internet protocol, version four, we're not talking about IPv6 because let's not kid ourselves, no one's really using that at scale despite everyone claiming that it's going to happen real soon now.

So there are roughly 4 billion IP addresses and change, and those are allocated throughout effectively the entire internet. When this stuff was built back when it was just defense institutions and universities on the internet, 4 billion seemed like stupendous overkill. Now it turns out that some people have 4 billion objects on their person that are talking to the internet and all chirping and distracting them at the same time when you're attempting to have a conversation with them.

So those networks are broken down into subnetworks or subnets, for lack of a better term. And they can range anywhere from a single IP address, which in CIDR, C-I-D-R parlance is a /32 to all 4 billion and change, which is a /0. Some common ones tend to be /24, which is 256 IP addresses, of which 254 are usable and you can expand that into 512 with a /23 and so on and so forth. The specific math isn't particularly interesting or important and it's super hard to describe without some kind of whiteboard. So smile, nod and move past that. So then you have all these different subnets. How do they talk to one another? I mean the easy way to think of it is, "Oh, I have one network, I plug it directly into another network and they can talk to each other."

Well, sure in theory. In practice, it never works that way because those two networks are often not adjacent. They have to talk to something else, go through different hops to go from here to there to somewhere else, to somewhere else to finally the destination it cares about. And when you take a look at the internet as being this network that spans the entire world, well that turns into a super complicated problem because remember, the internet was originally designed to be something that could withstand a massive disruption generally in the terms of nuclear war where effectively large percentages of the earth were no longer habitable, had to be able to reroute around things and routing is more or less how that wound up working.

The idea that you could have different paths to get to the same destination and that solves an awful lot. It's why the internet is as durable as it is, but also explains why these things are terrible and why everyone is super quick to blame the network. One last thing to consider is network address translation. They're private IP address ranges that are not reachable over the general internet, anything starting with a 10 for example, the entire 10/8 is considered private IP address space. Same with one 192.168, anything in that range is as well and anything between 172.16 and 172.20, give or take, if I'm wrong, don't at me. It's been a very long week and translating those private IP addresses into public IP addresses is known as network address translation or NAT. We're not going to get into the specifics of that at the moment, but just know that it exists.

Now, most of the traditional networking experience doesn't come from working in the cloud. It comes from working in data centers, a job that sucks and some of the things that you learn doing that are tremendously impactful. They completely change how you view how computers work and in the cloud, that knowledge becomes invaluable. So let's talk a little bit about what it looks like in the world of cloud, specifically AWS, because AWS had effectively five years of uninterrupted non-compete time where no one else was really playing with cloud. So by the time everyone else woke up, the patterns that AWS had established were more or less what other people were using. This is the legacy of Rip Van Wrinkling through five years of cloud. If you don't want me to talk about AWS and talk about a different company instead, that other company should have tried harder.

In AWS context, they have something known as a virtual private network or a VPC, and planning out what your network looks like in those environments is relatively challenging because people tend to make some of the same mistakes here as they did in data centers. For example, something that has changed is that common wisdom in a data center is that anything larger than a /23 or a subnet that has 512 IP addresses in it was a complete non-starter because at that point that is a large enough subnet that your broadcast domain or everything being able to talk to everything is large enough that it was going to completely screw over your switch. It would get overwhelmed. You'd wind up with massive challenges and things falling over constantly, so having small subnets was critical.

Now in the world of cloud, that's not true anymore because broadcast storms aren't a thing that AWS and other reasonable cloud providers allows to happen. It winds up getting tamped down. There are rate limits. They do all kinds of interesting things that mean that this isn't really an issue. So if you want to have a massive flat n...

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Networking in the Cloud Fundamentals, Part 1