An example scenario: You registered your domain previously and you're now ready to develop your new website, so you purchase your PageUP Productions hosting account and change the name servers for your domain to NS1.PAGEUPPRO.COM and NS2.PAGEUPPRO.COM. You wait a while for the name server changes to take effect, and then you visit your website. But for some reason you're still being forwarded to the same page as before, rather than the new server. This usually happens because of IP address caching, also called DNS propagation.
What's happening
When a website is requested through a web browser (Chrome, Internet Explorer, Firefox, etc), the request is first sent to your Internet Service Provider (ISP, such as Verizon, AT&T or Roadrunner). Your ISP then uses your domain's name servers to look up the location (IP address) of the web hosting server. Caching happens because your ISP, your web browser and your computer's operating system keep a list of already looked up IP addresses. These temporary lists are used to speed up future IP address look ups, so that web pages will load faster. This also helps to reduce the traffic on the Internet. Unfortunately, it can also lead to delays during name server changes.
Viewing your cached website
While DNS propagation is in progress your website will 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 repeatedly click 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 of your website 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, you may just have to wait up to three 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.
