No time to learn DNS but you need to know how it works? Learn how DNS works in this short overview video. Learn about the DNS hierarchy. Learn about DNS records. Learn how DNS makes the Internet work. Learn why DNS is at the backbone of all that runs on the internet. Learn how ecommerce and other important internet economy technologies only work because of DNS.
- [Voiceover] From Desktop support to the CTO, everyone who works in IT should have a fundamental understanding of how DNS works. This short video aims to help you in whatever your position to understand, how DNS functions. DNS, which stands for Domain Name System, is a hierarchically organized server based system. That functions very much like a Distributed Automated Contact Database. But instead of names and phone numbers, or names and street addresses, it keeps track of domain names, and IP addresses, and similar information.
If you can imagine a phone book or a book of contacts, you would expect that, that book would contain the names of people, and their addresses, and maybe phone numbers, and perhaps, information about your relationship with that person. Now, imagine that in the world of Computer Networks there are address books like that, which contain the names of the things you want to find on a network, like the Internet or your personal network. Imagine that those names would be listed with an IP address that tells you, what address to go to, if you want to access the resource with that name.
Similarly, it would be useful if that contact book could help you mail things to that address, and even tell you where the mail boxes are that accept mail for the address. Well DNS does all of that and more. If you think about how many possible IP addresses there are in the world, and that you may want to work with any one of them. You can see how keeping track of those tens of millions of individual addresses, would be hard if we didn't have this magical ability to give those resources names instead, to help us remember and find them.
So, what is Domain Name? Well, If you're in a Web Browser and you type the address of a site you want to go to, you are typing that Domain Name. Here's how that looks, at the end of a typical Web URL, you have a slash. Once you start navigating the site then there is more, but the Domain Name ends at that point, with that single first slash. And at the end, it is implied though not shown, that there is dot or period. That end point references what we call, The DNS Root Servers.
Those Root Servers are the address book in our metaphor that contain the information about all of the top level Domains. You know them as the .COMS or the .ORGS, the NETS or the GOVS. These top Level Domains are then followed to left, by another Domain. This next Domain is your Domain, the one for the organization your accessing, probably. This could be things like Lynda, or Apple, or Linked-In, or like our example here, DRDT.
That Domain is followed to left by another dot, usually. And then frequently, the last name, as we travel from right to left, is the host, at that Domain that we want to access. Which for a website is typically the WWW Server, but could the name of any Host. As in our example here, with the Server named Mail. That gives the FQDN, or Fully Qualified Domain Name of the server. A Domain Name is fully qualified if it ends in a Dot.
Which indicates the DNS Resolver, should ask the Root Servers for information to begin with. Nothing in the hierarchy can go beyond the Root Servers. And as that indicates the top level starting point for resolving the name, it's considered a complete name to serve as a request. This makes it, fully qualified. If you strip away all of the stuff from a Web Browser URL Field and just look at the Domain Name, you see the fully qualified Domain Name of the server, even if that Dot isn't shown to you in the interface you have.
If your DNS server hides the trailing Dot from you that may be confusing but dont worry, it's still in there with the Configuration Files. Another way you interact with DNS will show all of this very clearly. E-mail Addresses always have the Domain Name to the right of the @ symbol. And DNS's use to do everything from finding out what server handles mail for that Domain, to actually resolving the IP address for that server so it can deliver the mail. When it's done, what actually goes to the receiving server looks more like, this Sean @ an IP address you see here.
So to review, from right to left the URL tells DNS to look for the Root Servers. Which nowhere to find in this case, the ORG Servers but any Top Level Domain will do here. Followed by the names servers responsible for, in this case, DRDT. And when DNS finds the name server responsible for DRDT, It just asks, "Hey, where is the WWW Server at?" Or if you were looking for mail, "Where is the Mail Server?" And because DRDTs name server has that information, it responds with the servers IP address, enabling the client to find the Server it is requesting.
Now each of these levels is called a zone. And in fact, for any single zone there may be, many individual name servers responsible for that zone. For small zones, usually only one or two Servers will have authoritative information for that zone. For the Root Zones however, it's lots more. And in fact, more than just one organization is responsible for the whole zone. DNS Servers are obviously, incredibly important to how our devices find the resources they need to function, on a Network.
To begin, author Sean Colins covers the fundamentals of DNS. He then segues to more complex topics such as setting up a DNS server on Linux, Mac, and Windows and working with DNS record types, such as AAAA, MX, TX, CNAME, and SPF. He offers breakdowns of difficult concepts as well as practical technical tips for the day-to-day activities involved in DNS server management.
- How split-horizon DNS works
- Lookups in Network Utility and Terminal on OS X, and from the cmd prompt on Windows
- Resolving DNS from different DNS servers, including BIND on pfSense and DNS Manager in Windows Server 2012
- Query, recursion, and caching basics
- DNS hierarchy
- Root-level DNS servers
- Configuring resource records: AAAA, MX, TXT, and more
- DNS tips and tricks for BIND, Windows Server, and Mac OS X Server
- Exploring DNS server options