DNS Propagation Explained

SkyStra
Feb 25, 2021

What Is DNS Propagation?

DNS propagation is the timeframe it takes for DNS changes to update everywhere on the Internet. Any change to a DNS record, such as an IP address update for a specific hostname or a nameserver change, can take up to 72 hours to propagate worldwide (even though it typically takes only a couple of hours). Usually, changes to A, CNAME, or MX records are instant due to low TTL (Time To Live) value, while nameservers (NS) changes can take longer.

The reason for this behavior is that each time the change happens – all ISP (Internet Service Providers) nodes across the world have to update their cache with the new DNS information. Each ISP has a different cache refresh interval, so some will update sooner and some later.

If the visitor performs a DNS query and reaches a server where the cache wasn’t updated yet – that visitor will receive the old IP address, which means that the change has not yet been propagated to reach that user. 

There is no definitive way to know when the propagation has been 100% complete, which is why we always recommend waiting for 24 hours after nameservers update before making any changes to your website.

DNS and Browser Cache

In addition to the ISP nodes cache, your computer also has its DNS and browser cache. Your computer can remember the “old” IP address for up to 48 hours, so it’s always a good idea to clear your computer DNS cache before testing your website after the DNS update.

Browser cache isn’t related to DNS, but it can cause you to see the old content in your browser after the change. Browsers often cache a copy of the page you viewed previously, so it’s recommended to try clearing your browser’s cache after updating DNS.