Flush DNS

I set up a web site for my client yesterday, and the site was working perfectly on my end. However, my client claimed that he could not see the site.

This is not the first time my client went into this situation, so I would like to write an article to clarify what the problem is, and how does the DNS system work.

Before we going into the details, let me post the solution here in case someone else also run into this problem:

Click on start menu, and type in cmd in the search box

Right click on the cmd.exe icon found, and select Run as administrator

Accept the UAC privilage elevation request

Type in ‘ipconfig /flushdns’ in the command line window and press enter

Try again and you MAY find the problem is gone

So now let’s dive in to find the root cause.

The DNS system is distributed, combined with 1000s of servers that holds the DNS record (named Authoritative Name Server), servers that caches the answers, and clients. Each cache record was controlled by the TTL (Time to Live) property, and will expire normally after 24 hours or so.

How should I find out that I need to flush the DNS cache?

Go to command line window and ping your domain name. If the IP address is not correct and you are sure that the DNS setting are already set, you should try to flush DNS cache.