Maximum number of DNS clients store the results of all name requests in the cache. While browsing it is a common practice for multiple lookups to be done for the same address and this helps speed up name resolution. In case a bad DNS entry is cached, then one needs to either wait for 24hrs till it is automatically dropped from the cache or you need to flush the DNS.
Flushing DNS in Windows –
The command ipconfig/flushdns can be used in Windows for flushing of DNS resolver cache:
C:>ipconfig/flushdns
Windows IP configuration
Successfully flushed the DNS resolver cache.
How to turn off DNS caching in Windows –
DNS caching can be disabled, in case frequent issues are experienced with it, by using one of the following commands –
· Sc servername stop dnscache
· Net stop dnscache
DNS caching will be disabled, until the next reboot, by this command. The service tool or the service controller tool can be used to make this change permanent by setting the DNS client service startup to disabled.
DNS caching tuning in Windows –
In Windows the DNS caching algorithm behavior can be modified by setting the 2 registry entries in
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesDnscacheParameters registry key.
The maximum time until which the results of a DNS lookup will be cached is represented by the MaxCache Ttl. Its default value is 86,400 seconds. DNS entries will be cached only for 1 second if this value is changed to 1.
The maximum time of the caching of the results of failed DNS lookup is represented by MaxNegetiveCache Ttl. Its default value is set at 900 seconds. Failed DNS lookups would not be stored in cache if this value is set to 0.
Flushing DNS in Mac OSX –
DNS resolver cache can be flushed in Mac OSX by using the command dscacheutil –flushcache.
bash-2.05a$ dscacheutil -flushcache
The same task is performed by the command lookup-flushcache in Mac OSX versions 10.5.1 and before.
bash-2.05a$ lookupd –flushcache
Flushing DNS in Linux –
The DNS cache is managed by the nscd deamon in Linux.
The nscd deamon needs to be restarted in order to flush the DNS cache.
The command ‘/etc/init.d/nscd restart’ is used for restarting the nscd deamon.
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