What is DNS Propagation?

If you are working on the internet with domain names and websites, you will probably face the day where this new nerd phrase will appear: “dns propagation”. Let’s introduce the concept and why it takes so long for all people who is migrating websites from one server to another.

What is DNS propagation time?

When you migrate a website over one server to another, the last thing you must do is to update your name servers for the domains you are migrating. This needs to be done in order to map your domain name to the new server where you are hosted, otherwise none will notice you are hosted on a new network/hosting.

And that nameserver / dns change, can take up to 24-72 hours to fully take effect for all world wide users. This is what is called DNS propagation time or DNS resolution time.
In clear and simple words, is the time that it takes for ISPs from all over the world to overwrite their DNS caches and notice that your domain is now hosted on a new / different server.

During this NS propagation time, some of your visitors will see your site from the old server, while others (the ones who use ISPs were your new dns are already propagated) will see the website from the new server. This is totally normal, and it is part on how dns propagation works.

Why does it take up to 72 hours max?

DNS Propagation takes up to 72 hours because all ISPs from all over the world must update their DNS cache, and this takes time, because the NS change must be replicated in several ISP nodes first, before arriving to the final ISP destination. There are lot of intercontinental connections that makes this possible, but it can take some time.

Each ISP (Internet Service Provider) in the world maintains its own caching DNS server/s to speed up dns queries and reduce server load. Due to this, DNS servers store dns records in their local cache, and this cache has a TTL (time to live) that defines the time where it will check again to see if your dns records for your domain has changed or not. Until all ISPs have their TTL expired and all is propagated across the network, your domain will still be responding to the old server from that particular ISP.

Imagine the same process with the rest of the ISPs in the world, that’s why it takes up to 72 hours.

How can I test my DNS propagation across the world?

There are several ways to test your NS propagation, the first one and easiest is using your local computer terminal, from Windows, Linux or Mac, open a terminal and type:

ping yoursite.com

This will give you the IP provided by your ISP, for example:

[webtech@localhost ~]$ ping nixcp.com
PING nixcp.com ( 56(84) bytes of data.

You will notice the first line contains the IP address, that is the propagated IP at this exact moment.

If you need to run a global check, you can also use tools like this dns propagation checker, which is free and can give you instant results from world wide regions.

About the Author: Esteban Borges

Experienced Sr. Linux SysAdmin and Web Technologist, passionate about building tools, automating processes, fixing server issues, troubleshooting, securing and optimizing high traffic websites.