If there is one thing everyone knows or have at least heard about it is the internet. But very little know what holds the internet together “DNS”. Without DNS we would be stuck trying to remember all the ipv4 based ip addresses of our favorite websites and within the next few years ipv6 addresses, oh my I shiver from fear just having to think about such a thing. DNS allows all of us to go to our favorites sites by name such as www.digitalrage.org so that you can read about the latest in Information Technology. Having been in this field for over 15 years now I have seen this question asked on BBS’s (remember those flash from the past ?), newsgroups, mailing list, and forums. Often website and dns admins have to change records which might cause problems like reachability due to the fact that just about all clients now cache dns locally so until it ages out you may think that your favorite website or page you are trying to get to is down. Having seen this so many times and being asked this by users of networks I have supported in the past I thought this would be a great first HowTo for my site.

As I stated most DNS clients cache the results of name resolution requests locally. This speeds up name resolution if multiple lookups are done to the same address, such as returning to the same website or when checking email something we all do. If bad a DNS entry is cached it can cause frustration and sometimes stress when this evolves around business related apps. Before being overwhelmed with frustration and stress try flushing the DNS cache from the local pc to get rid of it, or wait up to 24 hours or longer for it to be dropped from the cache automatically.

How to Flush DNS in Microsoft Windows
In Microsoft Windows, you can use the command ipconfig /flushdns to flush the DNS resolver cache.
You can also use the command ipconfig /displaydns to view the DNS resolver cache.
Go to start, run type in cmd or command for older Windows O/S’s like win95.

C:\>ipconfig /flushdns

Windows IP Configuration

Successfully flushed the DNS Resolver Cache.

How to Flush DNS in Linux

In Linux, the nscd daemon manages the DNS cache.

To flush the DNS cache, restart the nscd daemon.

To restart the nscd daemon, use the command `/etc/rc.d/init.d/nscd restart`.

In SuSe Linux the rc.d directory is linked to init.d so it will be done the following way

SuSElinux:# /etc/rc.d/nscd restart
Shutting down Name Service Cache Daemon done
Starting Name Service Cache Daemon done

And last but not least Mac OSX. I knew i had to include this O/S or a certain close friend of mine would never let me live it down. Not having had very much experience with this O/S I had to ask a coworker in the graphics department this question
How to Flush DNS in Mac OSX

In Mac OSX, you can use the command lookupd -flushcache to flush the DNS resolver cache.

bash-2.05a$ lookupd -flushcache

And for the Sysadmins we all know that this Book should be on all of your bookshelves.

–Elijah