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There can be several reasons as to why your website is not yet displaying. This article is a technical introduction to DNS and nameservers, with a focus on how they work in the context of web hosting.
- You recently registered your domain in your AccountCenter. Please allow up to 24-48 hours for your domain to fully propagate across the Internet. This is called DNS Propagation.
- You did not add your domain to a hosting server. Please see this article for instructions and screen shots: How do I add a domain or subdomain to my server?
- Your domain was registered elsewhere but you have not yet pointed the nameservers to (mt) Media Temple. You will need to update the nameservers to:
Please allow up to 24-48 hours for your domain to fully propagate across the Internet.
What is DNS?
DNS stands for Domain Name System. DNS is the mechanism that translates Internet domain names, such as example.com, into IP addresses, such as 188.8.131.52.
When you want to visit a website, you will typically type in something like example.com. and then expect to see some content in your browser. This website content is pulled from a server in a data center somewhere - if you're using (mt) Media Temple hosting, we provide the server and the data center. But how does the internet know that it should pull content from one particular server when you type example.com in your browser? The first part of the answer is that the network layer of the Internet uses one or more IP addresses to identify each server. The second part is DNS. DNS allows domain names to be mapped to those IP addresses, so that when a certain domain name is requested, the right IP address is found, and the right server is queried for the website content.
DNS is handled by special servers called nameservers, or Servers of Authority. Nameservers contain a zone file for each domain. The zone file lists the IP addresses that each domain uses for basic web requests, subdomains, email traffic, etc.
A nameserver is like a phone book for your domain, where the IP address is your phone number. The zone file is like the actual printed listing in the phone book.
More about DNS nameservers
DNS uses many different nameservers in a hierarchical structure, so that DNS queries are executed efficiently. At the top are 13 special DNS nameservers called root nameservers. The root nameservers have listings for the next set of nameservers, which are responsible for top-level domains, like .com. .net and .edu. Eventually it gets down to nameservers with individual domain name entries and zone files. (mt) Media Temple provides nameservers like this, with individual zone files for specific domains.
When you request a domain name from your browser for the first time, your computer sends a request to one of the root nameservers. The root nameserver looks at the top-level domain name, and returns, for example, the nameserver responsible for .com. Your computer then contacts that second name server, and repeats the process until it reaches the nameserver that actually has the zone file for the domain. Once your computer reads the zone file, it can find the IP address for the domain, connect to the correct host server, and display the website content.
This process is often abbreviated by Internet Service Providers, who cache IP addresses for recently-requested domain names for a few hours (typically 24-48 hours).
For your domain name to be available over the Internet, you must have a zone file registered with at least two nameservers: a Primary/Master nameserver and a Secondary/Slave nameserver (or backup nameserver). You can typically use nameservers provided by either your registrar or your host. (mt) Media Temple provides NS1.MEDIATEMPLE.NET and NS2.MEDIATEMPLE.NET as nameservers to all hosting customers as a courtesy service.
Reverse DNS and PTR records
Nameservers are responsible for both name-to-IP-address translations (called forward lookups) and IP-address-to-name translations (called reverse lookups). That is, you can also find the host name of a machine based on its IP address.
For historical reasons, the way this is done is to create a dummy top-level domain (similar to .com or .net) called .in-addr.arpa.
Domains have top-level domains like .com, and IP addresses have subnets. For example, the IP address 184.108.40.206 is part of the 64.207 subnet. To perform a lookup on an IP address (also known as a reverse lookup), the IP address must first be reversed. For example, if you want to know the host name corresponding to 220.127.116.11, you would first ask the in-addr.arpa nameserver for 18.104.22.168.in-addr.arpa. The in-addr.arpa nameserver could then hand off your request to the 207.64.in-addr.arpa nameserver. That server might in turn hand off the query to the 129.207.64.in-addr.arpa nameserver, which would finally give you your name.
To set a custom reverse DNS record for your IP address, your registrar or host must allow you to control its DNS. The file with the reverse DNS record is known as a reverse zone file.
Some customers prefer to run private nameservers. All domains must be registered with at least two nameservers. However, you may not want to pay for two actual servers to act as nameservers. As long as you have at least two IP addresses on your server, you can set up two virtual nameservers to fulfill this requirement, although this is less foolproof, as both will be unavailable if the server stops serving DNS. See DV:Set up private nameservers for details.
Managing (mt) Media Temple DNS
For more complete information on DNS, we recommend the following books:
- DNS and BIND. by Paul Albitz and Cricket Liu, O'Reilly & Associates, 5th Edition, April 2001
- TCP/IP Illustrated, Volume 1: The Protocols. by W. Richard Stevens, Addison-Wesley, 1994