This article was written for ThinkDoBeCreate by Christopher Shepard of WebHost Gear, a site that provides hosting information and reviews of major web hosting providers as well as website development articles and tips.

So you’ve done everything you can think of to launch your website, and share it with the entire World Wide Web. You registered a domain name. You paid for web site hosting with the hosting provider of your choice. You uploaded the contents of your website to your web server. You’ve done all this, yet you still can’t see the results of all your hard work! When you ask around you’re told that it has to do with something called “DNS propagation”. What the heck is “DNS propagation” and what does it have to do with not being able to see your web site?

To understand what DNS propagation is, you first need to understand how DNS works. DNS stands for “Domain Name System”. When you first set up a web site with a web host, they create what is called a “Master DNS Record” within their DNS servers. Your domain name registrar—the company that paid to register ownership of your domain name—then indicates your web host’s DNS server as the master authority of your domain name.

No matter where you host your website, the network your site is on has its own DNS server. In fact, it is standard for most web hosts to have two or more DNS servers. These servers then act as the authority for your domain; your Internet service provider makes a couple of entries in their DNS server: one is for your domain name that basically says: “YOU ARE HERE!” Technically, this is called an “A” record—“A” stands for “address”. The other entry is called the Mail Exchanger (MX) record, which designates a mail server that will receive emails for your chosen domain name.

There are hundreds of thousands of DNS servers located worldwide. Each DNS server is sort of like an address book for the Internet. They have information about your domain name, which acts as your address for the Web. Remember though that no single DNS server has all of the domain names for the entire Internet. They only have the names they are responsible for. Some DNS servers do nothing but store domain names. Other DNS servers provide “look up” services for computers to look up domain names. Still other DNS servers do both jobs.

There are a few bits of important information kept on a DNS server about your domain name. All of this information taken together as a whole is called the “DNS Record”. In the DNS Record, computers can find other bits of information, also called records, regarding your domain name. For DNS propagation, the only part we need to understand is the part that stores the ‘A’ record.

When an visitor types in a domain name, the computer then accesses the registration database to ask about the DNS authority for your web site (the DNS servers of your site assigned by your web host). Then they visit these DNS servers for the IP Address for your domain name (it’s sort of like the street address for a building, also assigned by the web hosting provider), retrieves all the information from that IP address, and delivers it to the visitor in the form of the web site.

The problem with this set up, though, is that to speed up the rate at which a customer can view the World Wide Web, every Internet Server Provider (ISP) will cache their DNS records. What that means is that an ISP makes their own copy of the master domain records, and will read from those locally saved copies, instead of looking them up over Internet every time someone wants to look at a website. This actually makes web surfing faster by speeding up the time it takes for your web browser to look up a domain name and get the record, and reduces the amount of overall traffic on the web, thereby giving the web the ability to load faster.

The drawback to this caching method, and why it can take so long for a website to be viewable to everyone, is that each ISP that caches its DNS records only updates those records every couple of days. The time between updates isn’t set to any particular standard. Each individual ISP can set the update time to be anywhere from a few days to a few hours. This slow update of the cached records is called propagation. It’s so named because after you register your web site, the web site’s DNS information is then propagated across every DNS server on the Internet. When this process is finally complete, everyone is able to visit and see your new web site. Since the cache time is different for every DNS server, DNS changes can take from 36 to up to 72 hours to be totally updated.

So the next time you set up a new website and you don’t see it right away after you upload everything, or you’re not receiving emails sent to the email addresses tied to your website, don’t panic—your website wasn’t killed on sight and neither is your mail server. The information is just currently being sent, copied, and cached to every possible DNS server in the world, and the world is big. Wait up to three or four days—it usually doesn’t take longer than that. Push website launch dates back a couple of days, in order to give time for DNS propagation to complete.

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