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DNS 101: What Is A Hostname?

As part of my Implementation Specialist duties, I help train sales folks with a basic knowledge of DNS, Email and our various service offerings. I’ve been doing this for a while now and routinely get the same question after a few weeks: “I think I’m starting to get this, but what’s a hostname?”

While this can be explained from a business logic point of view, you need to take a quantum leap to understand the technical aspect. Given the popularity of the question, I thought it would be fun to go over for our community.

I would describe a hostname as a human-friendly label to easily remember a specific location on the Internet. DNS records can then be added to the label to perform a function, most commonly an IP address.

There are a few other terms in DNS land that sometimes gets confused. To explain where they all fit, let’s go step-by-step in a full DNS lookup for the hostname www.dyn.com.

Root

All journeys have their beginning. In DNS, this is at the root, signified as a period ‘.’. Root says he doesn’t know the answer, but sees that the next link is com and knows right where com lives (they hang out sometimes, play poker on Tuesdays, that sort of thing).

Top Level Domain (TLD)

com is a top level domain on the Internet. There are many different TLDs for countries, organizations, governments or generic purposes, such as .org, .au, .biz. At this point, com still doesn’t know the address we are looking for, but knows that ns1.p01.dynect.net is the authoritative DNS for the whole fully qualified domain name of dyn.com, so they must know where to go!

Fully Qualified Domain Name (FQDN)

dyn.com is the fully qualified domain name that contains the namespace which www.dyn.com lives in. DynECT Managed DNS, its DNS provider, has heard of www.dyn.com and directs our query right to them.

Subdomain

www is a subdomain on dyn.com, and contains the record 204.13.248.106. Finally, we can connect to the IP address and carry on with our Internet experience. While seems like a detailed process all happens in miliseconds.

So that is what the terms mean within the Internet, but what are those zones and nodes we are always talking about?

Zone

The zone is the DNS information on a namespace, typically a domain.

Node

A node in the purist sense is just a part of a system. If the zone is our system, nodes are just the parts that make it up. Nodes are the DNS equivalent of subdomains — divisions of the whole space to direct traffic to different places.

When I explain all this, this is usually where I get the, “Hey, this is starting to make some real sense but we covered all these topics and still never got to hostname. You’re killing me here, Matt. What is a hostname?!”

Hostname

A hostname is nothing more than the path back to root. This can happen anywhere within this chain. So dyn.com is a hostname, and www.dyn.com is a different hostname. These can all affect traffic in different ways and might require different services to get the job done.

vpn.dyn.com might have an Active Failover instance. www.dyn.com might have a Traffic Manager and the apex of dyn.com could have a HTTP Redirect. These all work in unison without stepping on each other because they are all different hostnames.

Another way to think about it is that a hostname is what you put into your browser to bring you somewhere on the Internet.

Hopefully that helps make some sense, as we use hostnames all the time. Now you know exactly what they are and can wow your fellow co-workers, friends, dry cleaners and traffic cops with this new information!

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Whois: Matt Torrisi

Matt Torrisi is Solution Architect at Dyn, the world leader in Internet Performance Solutions that delivers traffic management, message management, and performance assurance. Follow on Twitter: @DrFuzz42 and @Dyn.