Domain Name Server (DNS) Propagation
Here is an example scenario: You registered your domain, and it's set to parking. The time comes when you decide to develop your website, so you buy hosting and set your domain to use your web host's name servers. You wait around for a while for the name server changes to take effect, and then you visit your website. But for some reason, you're being forwarded to www.dynadot.com. If your domain wasn't previously using parking, then you might be seeing your old web site. This usually happens because of IP address caching, also called DNS propagation.
When a website is requested through a web browser (Internet Explorer, Firefox, etc), the request is first sent to the computer's Internet Service Provider (ISP) which contacts the domain's name servers to look up the location (IP address) of the web hosting server. Caching occurs when the web hosting server at the IP address location no longer hosts the website, but a visitor's web browser still attempts to connect to that server to retrieve the web page. This happens because the web browser and the computer's operating system keeps a list of already looked up IP addresses, and it refers to that list for future IP address look ups. ISPs also keep their own IP address list as well. The purpose of this is to speed up web page loading times, and to reduce the traffic on the Internet. Unfortunately, this can lead to delays during name server changes. The images below shows what happens when there is no caching and what happens when there is caching.
No caching- This is the type of lookup that happens for someone visiting your website for the first time, or if they haven't visited your website for a while.
Caching at the ISP level - ISPs keep a list of already looked up domains. This list is only kept for a couple days. If a name server change is made, the ISP won't look up the new IP until the IP kept on the 'Already Retrieved' list expires. So in the example below, if ns1.your-new-host.com says 'www.yourwebsite.com is at the IP address 220.127.116.11,' the website visitor will not receive that information until the www.yourdomain.com IP on the 'Already Retrieved' list expires.
Caching on your computer.- Even your computer and your web browser cache IP addresses. That way, there's no need to go out on the Internet to look up the IP address, which saves time. But during a name server change, your computer may still go to the old IP address for a few days.
How to check if your website is cached
Dynadot has two very useful tools for determining if your website IP address is cached. The first is our IP Lookup Tool. The IP Lookup Tool will tell you if your new name server settings are working properly. It will also show your name servers and the domain's IP address in real-time, without any caching. The second tool is our Snapshot Tool. The Snapshot Tool uses the real-time IP address to retrieve the home page of your website. If the snapshot shows the page you're expecting, but you don't see the same page when viewing your website in your web browser, then it's probably because the IP address is cached.
Viewing your cached website
Your website will still work properly for new visitors or infrequent visitors. To get it working for you, there are a couple things that you can try. You can try repeatedly clicking your web browser's refresh button while viewing your website, or you can try clearing your web browser's cache. You can also try restarting your computer. Windows users can clear their OS cache by using the 'ipconfig /flushdns' command. If the previous methods don't work, then the IP address might be cached by your ISP. In that case, you can try contacting your ISP and asking them to clear their DNS cache. If all of the above don't work, then you may just have to wait 1-3 days for the cached IP to expire.
In the mean time, you can visit your domain from a different ISP, perhaps at work, a library, or a coffee shop. Hopefully, the ISPs and computers at those locations haven't visited your website before, or at least not recently enough to cache the IP address. Eventually though, the cached IP address will expire and the real-time IP address will be looked up and used to connect to your website.
For more information about Dynadot's IP Lookup Tool and Snapshot Tool, click here.
Related topics: Domain Name Articles