What are DNS Zones And Records? transcript

Today we're here to learn about DNS zones and records. First, let's start with a quick review of the DNS. As you may remember, DNS is the protocol that's used to convert the name that someone typed in their browser into a number that the computer can understand. So for example, the user types www.ibm.com, their PC talks to the local resolver, which then goes out to the DNS, to an authoritative DNS name server who looks up that name, www.ibm.com, and returns the IP address for a www.ibm.com, and then the user is able to get to the web page for IBM and go view all of our products.

Now this all works great, but you may be now responsible for DNS and need to set it up for your particular application. So you're wondering, what are these things that I'm hearing about? Zones, RR sets, all those different terminology. What is what does it all mean and how do I use it? So let's start at the beginning with, "what is a zone?" So a DNS zone is an area of administrative control of a portion of the DNS namespace.

So for example, we might have a zone for ibm.com. And inside the zone we're going to have a number of records. And records are things like www, would be the record, the type is IN, and I'll go over all this in more detail in a minute, it's an A record type, and the IP address is 9.9.9.1. Now I might have another record, also www, actually I did 4 w's ... IN, A, and it's 9.9.9.2. What this means is that there's two records with the same label, with the same name.

And that's called a resource record set. You'll often hear that, in the DNS terminology. All it means is that there's multiple records with the same name but different values, different answers. Want to also mention here a special record type called a Nameserver record, and that's used to do what we call delegate the zone to another group. The use case for this is, for example maybe the central CIO team is managing ibm.com, but there's another group for which you want to give access to a portion of the DNS, and you want to give them their own zone on their own server.

So in that case you'll set up a special record type called Sub Zone. That's this is the name. It'll point to a name server record, NS, and we'll just say it's going to subzone nameserver.ibm.com. Now, what that does is it creates this redirection to another zone called subzone. Subzone.ibm.com. And then here we can also set up records. So say maybe that team wants to set up an API. So they create a record API, also an A record, and it points to 9.9.10.10.

So when someone does a lookup over there for api.sz.ibm.com, it will first go to this zone, which will then redirect it via this NS record to a subzone where it will find the answer API.subzone.ibm.com and return 9.9.10.10. So that's an overview of zones, which are an area of administrative control of a portion of the DNS namespace, and records which are the entries or the rows in the database that actually provide the data.

So now let's talk a little bit about the different types of records that are available. So if I go over here and let's talk about the format of records. So records have a number of fields. First they have the owner field, which is like the www. They then have a class. So let's fill this in as I go, so this is www. The class would be IN. There are a number of classes defined, but the only one you'll ever see used is IN, which stands for internet.

The other ones are mainly experimental, or are used for odd use cases which you almost never see. Then we then have a type. The most common example you'll see is the A record, and then you'll have a value. And the value is the number here, 1.1.1.1, for example. Let's go through a few different types, just to give you a feel for what are the types out there. I'm not going to cover them all. But before I get started, I want to refer you to a website, iana.org That's the official body that maintains the list of all the different record types, and you can go there and see the full list of what's available.

But I'll cover the main ones that people tend to use. So the next one we have is called the Quad record, which is written as four A's. And it's for an IPv6 address. So something like 2001::1:2:7 would be an IPv6 address. Another common type we have is the mail server address, which is an MX record. That has two portions to the value. It's got a priority and the mail server name. So something like mail.ibm.com. It allows you to set up multiple name servers.

So maybe I have another one that's priority two, that's maybe mail2.ibm.com. What that means is that the sender will first try the priority one entry. If that doesn't work then it'll try the priority two entry. So there's kind of built in redundancy enabled through the DNS. Another common type is called the CNAME. So if I have one, just take label foo and CNAME. And this one stands for "canonical name". It's essentially a redirection.

So in this case if someone types in foo.ibm.com, I'll redirect them to www.ns1.com. And that's just a straight text replacement. foo.ibm.com gets replaced with www.ibm.com. You'll often see this used when you're deploying your website into a CDN, where the CDN will provide you the value to use for your canonical name, or your CNAME record. Another common one is a text record. And so if we have a record like this text and we can just say "hello world".

If someone types in types in hello.ibm.com, they'll get back the text "hello world". And the last one, which I showed over here, is just the NS record. Just for completeness, we'll add it in, and we'll have sz.ns.ibm.com. And again that's for delegating your zone to a different entity so that they can also work on the zone. Again these are just a few examples. Check out the site iona.org for the full list. And hopefully now you have a good idea of the terminology of DNS and you're on your way to becoming a DNS administrator.

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