About DNS (Rewrite)


The Internet’s directory was once a simple text file on a single computer but has evolved into many directories world-wide that enable the Internet as you know it.

Featuring Tom Merritt.



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Episode transcript:

In 1972, four years after the Mother of All Demos, Douglas Engelbart’s Augmentation Research Center might have felt like it was falling apart. More and more folks who had worked on Englebart’s NLS were moving on, many of them up the street to Xerox’s Palo Alto Research Centre.
But that didn’t mean Engelbart’s Augmentation Research Center was closing. Over the past few years ARC had been working with the Advanced Research Project Agency on its new network, the ARPANet. It had launched October 29, 1969, and had 29 computers connected but new hosts weren’t moving as fast. So Bob Kahn at ARPA wanted to show off to everyone what this network could do and why it was worth funding.
Kahn was planning a big demo of ARPANET at the first International Conference on Computer Communications in Washington, DC and needed someone to organize all the info into a handbook to go along with the demonstration.
Elizabeth Feinler, aka “Jake,” was a biochemist. But she was also fascinated with how to compile large amounts of data. She had worked on a project to index all the chemical compounds in the world. And in 1960, joined the Stanford Research Institute where she developed the Handbook of Psychopharmacology and The Chemical Process Economics Handbook.
By 1972, she led the Literature Research section at SRI. And she told Webster University Professor Julia Griffey in 2019 that, of course, she knew Douglas Engelbart
So Engelbart asked her to come over to the ARC team where she wrote the Resource Handbook for the ARPAnet demo.
You don’t put together all the info about how the ARPANet works without becoming a useful resource people rely on when they have questions about how the ARPANet works. By 1974, Feinler was one of the people planning and running the Network Information Center.
NIC was the reference desk of ARPANet. You needed to know something you called NIC. Literally. On the phone. You could also send a letter if your request was less urgent. NIC published a book– the successor of that Resource Handbook from the demo– listing all the protocols of ARPANet and all the registered names and and terminals.
That demo had worked and more computers were connecting to ARPAnet all the time. In 1974, the network working group decided to create a text file to list all the host names, so they didn’t have to keep publishing a pamphlet. You had an information network after all, why not use it.
Feinler took charge of making sure it was updated. She’d keep doing that until 1989 when the domain name system came along and made it easy to find a machine on the now Internet just by typing in a name. Without it, Feinler at 92 might still be updating that hosts file.
So let’s help you Know a Little More about the Domain Name System, aka DNS.
DNS stands for the Domain Name System. It’s essentially the system that lets you type google.com when you want Google search rather than having to remember something like
That string of numbers is an Internet Protocol Address or IP address. That’s actually how computers on the internet talk to each other. They identify as numbers.
Domain Names are associated with those numbers. When you type in a domain name in a browser the browser goes and looks up in a table which number (or more often range of numbers) goes with that domain name so it can find it on the internet. The same way you just go to your friends name in your phone’s contact list to call them. You don’t tap in their phone number by hand.
The Domain Name System provides a worldwide distributed directory of which domain names go with which numbers. It’s not just one table (anymore) it’s lots of tables on lots of servers around the world. So DNS also defines a communication protocol for how all those directories communicate with each other so that any computer can find another on the Internet.
But it did start in 1974 as that HOSTS.TXT file on a machine at the Stanford Research Institute developed and maintained by Elizabeth Feinler. She mapped host names to the numbers she found in the Assigned Numbers List handled by Jon Postel at USC. Feinler and her team managed that list for the ARPANET– and later Internet– until 1989.
But along the way that host table became slow and unwieldy. And on January 1, 1983, the ARPANet and Defense Data Networks switched to the TCP/IP standard and became the Internet, That meant all networks could be connected by a universal language. It also meant a lot of safety nets that existed before were no longer there and there were a number of issues that needed addressing. Some of them were considered very important and got a lot of attention. Others not so much.
That’s Paul Mockapetris talking to the Oxford Internet Institute about taking on the task of automating and publishing the original spec for the domain name system in November 1983.
Four UC Berkeley students wrote a UNIX implementation of the spec called the Berkeley Internet Name Domain or BIND. BIND is still the most widely used DNS software on the Internet. And yes it has been updated several times since then.
The domain name system itself is made up of multiple domains. The most familiar is of course .com. There’s also .org, .net .fr .biz and on and on. Each of those domains has an authority responsible for assigning domain names and mapping them to the corresponding numbers. Each domain has multiple name servers that you can call on to find which domain name goes with which IP addresses.
But it’s not just one server with all the addresses. In fact the process involves different servers for different parts of the domain name.
You see the domain name itself consists of multiple labels. Let’s take knowalittlemore.com The right-most label is the top-level domain .com. Each label to the left specifies a subdivision. So the first to the left is knowalittlemore which is the domain of this show. For websites usually the last label is www to specify that you mean the web server on that domain. So when you type in http://www.knowalittlemore.com you go to the website for knowalittlemore.com not the email server. If you’re thinking you don’t type in www ever, well, browsers can add it for you and you can configure your nameserver to assume www was meant if nothing else (like say SMTP for email) is to the left.
Each label in your domain name can have up to 63 characters. A full domain name with all subdivisions can’t be longer than 253 characters in text or 255 octets of storage in binary.
The characters in a domain name are officially A-Z, 0 through 9 and the hyphen. However the Internationalizing Domain Names in Applications or IDNA system can map international characters into this set so locals can use their own alphabet.
Each domain, like .com. .uk. etc has a set of authoritative name servers that are either primary or secondary. A primary server has the original up to date copy of all domain records. Secondary servers communicate with the primary to automatically update.
In practice, information is cached to speed things up and you’re almost always calling on cached information when you browse. But let’s pretend there was no cache available and you want to go to knowalittlemore.com. The request would start by finding the closest root name server. These are spread throughout the world. The root name server would direct you to the nearest .com name server, that server would then tell you which IP address goes with knowalittlemore.com you’d check there to find out which server is the web server at knowalittlemore.com and potentially with more complicated requests, onward until you get the exact server you’re looking for.
With all these intermediaries it’s possible for malicious actors to figure out how to insert themselves and give you the wrong IP address for a domain that would then take you to a malicious version of the site that might look just like the real site but infect you with malware or something.
Domain Name System Security Extensions or DNSSEC requires each level of DNS server to digitally sign its requests to assure they haven’t been intercepted. It is deployed at the root level but has not been fully deployed across the system because of complexity and also reasons.
As I said, in practice so much of the process is cached, that root name servers get a very small fraction of requests, otherwise they’d get overloaded. Records may be cached in your browser, in your router by your ISP and so on. Cached records have a time to live set on their records so they are forced to go update and look for changes regularly so they stay pretty well up to date.
The name servers record more than just domain name and corresponding IP address. It also includes mail exchanges, known as MX records, domain name aliases known as CNAME as well as responsible persons, there’s even a real-time blackhole list or RBL for combating spam.
And it can do more than just tell you what domain name goes with what address. The DNS can provide the IP address that is closest to the requesting computer. This function is essential to cloud services and content delivery networks. Netflix doesn’t have one machine at Netflix.com. It has thousands and the Domain Name System is the first step in routing your Netflix app to the closest set of Netflix servers so you have the least delay in getting that episode of Stranger Things.
OK so I know a lot of you have questions about registering domains and how that fits in, let’s touch on that briefly.
To register a domain name and get its record created in the DNS directory you need to deal with an official domain name registrar. The registrar is different from the registry. Each domain like .com or .us has a registry. The registrar is contracted to handle requests for domain names and collect and verify the information that is then entered into the directory by the registry. Registrars can and do charge fees for this.
And yes registry and registrar are different and really should have been named something that made that a little more obvious.
Let’s use an example: for .com, authorized registrars – like say hover.com– must pay the registry – in the case of .com that’s Verisign. The registrar also pays a small administration fee to ICANN for each domain it handles. The price the public pays the registrar is these fees plus some markup. The maximum registration period is 10 years, though some registrars offer longer periods by legally binding themselves to renew the domain at the end of each ten year period.
There are usually more than one registrar per domain and in fact registrars usually handle more than one domain. Registrars can also authorize resellers as affiliates.
So there you have it. You pay a registrar to register a domain name with a registry and then when someone looks up your domain name the domain name system directory, or likely a cached copy of it, will point a browser to the IP address of your web server.
And Jake Feinler doesn’t have to be involved anymore.
Oh and one more thing. If you’re wondering why Elizabeth Feinler went by Jake, Feinler told the Computer History Museum in 2001, that when she was born in 1931, double names were a fad. Her middle name was Jocelyn, so they called her Betty Jo. Except her sister, Mary Lou, pronounced it Baby Jake. Eventually she grew out of the Baby, but the Jake stuck.
And we thank Jake Feinler for her hard work keeping that Hosts file going in the early days.
In other words, I hope you know a little more about DNS.

Know A Little More is researched, written and hosted by me, Tom Merritt. Editing and production provided by Anthony Lemos and Dog and Pony Show Audio. It’s issued under a Creative Commons Share Attribution 4.0 International License.