DNS Propagation SIMPLIFIED
Imagine a DNS (Domain Name Server) is a conductor that points someone in the direction of your business (Your website). When someone asks the conductor for the name of your business(Your domain name), they look up where your business is located and points that person to that business.
Since there are people all over the world using this system there need to be conductors all over the world. These conductors know where all of the businesses are in the world. However, they can not be reviewing all of the businesses all of the time. What they do is periodically check with the other conductors to make sure the business is still in that same place. If your business does move, it takes them a little time (up to 48 hours) to find out from the other conductors where the business is now located (your new website server).
When the IP (Internet Protocol) address for a domain is changed, there is usually a waiting period before all the of Domain Name System servers (DNS servers) across the internet holding the now incorrect IP address update to the new, correct one.
What is DNS Propagation (Technically)?
This is usually referred to as DNS propagation, although this is a technically incorrect term. DNS servers do not spread new information to other DNS servers, which is what the term propagation implies. Rather, they cache records with a certain Time To Live (TTL), and after they expire, they query other DNS servers for the current information.
Often, a time like 48-72 hours will be given as the total time for a propagation, but this can be complicated to actually estimate. DNS servers all up the chain cache the information for different times because they last queried for the information at different times, and then your individual computer will cache DNS entries and possibly your internet browser (Chrome, Firefox, Internet Explorer) as well. The “48-72 hours” number is usually taken from the default cache time for Top-Level Domain (TLD) DNS servers (like com, net, org).
So if you’re told your new site is live but you don’t see it quite yet, don’t worry! Let the internet get it’s act together, and eventually your new site will turn up.