DNS caching and name resolution results caches
Most computers have DNS clients which cache the results of name resolution requests. This speeds up name resolution if multiple lookups are done to the same address, such as is common when browsing the web, replying to email, or uploading/downloading files by FTP.Various spyware, malware and virus laden programs deliberately poison your local DNS cache in an attempt to hijack traffic, redirect you to their webistes, or fake you into parting with banking passwords etc.
Additionally it is becoming increasingly common for dial-up and ADSL ISPs to cache the results for extended periods (upto 7 working days) in an effort to cut down on the DNS traffic on their networks.
Sometimes an incorrect, missing or bad DNS entry will therefore be cached and you will need to either flush the DNS cache to get rid of it, or wait up to 48 hours for it to be automatically expired from the cache.
Should your local machine be returning a suspect IP address for any reason, you should verify the real IP and flush the cache from your machine/network.
How to Verify correctly resolved IP addresses
Use an external, 3rd party tool like www.samspade.org or dnsreport.com to lookup the correct IP Compare the result to your local DNS cache to see if your results are out of date or incorrect.How to Flush DNS in Microsoft Windows
In Microsoft Windows (XP, 2003, ME, 2000), you can use the command-line interface (Start, Programs, Accessories, Command-Prompt) command:ipconfig /flushdns
to flush your DNS resolver cache.
Use the command:
ipconfig /displaydns
to view the existing DNS resolver cache entries.
C:\>ipconfig /flushdns
Windows IP Configuration
Successfully flushed the DNS Resolver Cache.
How to Flush DNS in Mac OSX
In Mac OSX, you can use the unix shell interface (terminal) command:lookupd -flushcache
to flush the DNS resolver cache.
bash-2.05a$ lookupd -flushcache
How to Flush DNS in Linux
In Linux, the nscd daemon manages the local DNS cache. To flush the DNS cache you simply restart the nscd daemon with the command:/etc/rc.d/init.d/nscd restart
[root@ #]/etc/rc.d/init.d/nscd restart
