Being a server administrator I have to deal with a hell lot of ip address and domain names. One of the major problem that I face while configuring a server is sometimes I have to change ip addresses to different domain names for certain purposes and when you go to test if you have successfully established a connection or not the computer gives you an error just because it still has that old ip address in the memory and is constantly trying to connect to a dead ip.
This might be a useful feature for average users who visit Facebook and YouTube dozen of times a day as it reduces the time the browser takes to download pages from the servers of the websites by eliminating the need for a DNS server by caching the most visited url.
So if you are a server admin like me or are a newbie in this field and are facing the same problem clearing/flushing your DNS cache may do your job.
To clear dns in windows: Go to All Programs -> Accessories -> Command Prompt or Go to Run and type cmd. Once in there type
Mac and Linux both being UNIX based system have the same method to do this.
For Mac go to Applications -> Terminal
For Linux press Alt+F2 and type in gnome-terminal
Then give the command
This will clear all your DNS cache and should solve your problem If not have a look at your DNS server.