What is DNS Propagation?

You may have heard something like this before when launching or moving a website. "Your customers might see the old site or the new site until DNS propagation is complete, which could take up to 48 hours."

To understand why this happens, we first need to discuss DNS.

What is DNS?

Simply put, the domain name system (DNS) is the phonebook of the internet. One of its primary functions is to associate domain records with IP addresses.

If you want to call John Smith, you'd look his phone number up in the phonebook. If you want to visit chrisburge.net, your computer would first lookup the IP address of my web server.

DNS isn't a single phone book, however. It's a plethora of phone books that are constantly being updated. When you visit a website, your computer is only querying one of these phonebooks.

What is DNS Propagation?

DNS propagation is the process by which domain records are updated.

If I were to move my website to a new server with a new IP address, then I would need to update my website's domain record; however, it takes time for this updated record to work its way through the entire domain name system. This is DNS propagation.

Unfortunately, the delay caused by DNS propagation is non-uniform. The web server to which a visitor is taken depends on the DNS server his computer is querying. The record might be updated; it might not. The visitor might see your old site or your new site until DNS propagation is complete.

In Avoid DNS Propagation Lag When Updating DNS, I discuss two methods for address this issue.