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Windows 10 FlushDNS

One issue when cutting over services or performing datacentre disaster recovery operations consists of three little letters – DNS.

DNS records have a time to live (TTL) and depending on the zone file configuration, it could be several hours or even measured in days.  So if a record was changed, this means that in normal run state clients would continue to connect to the old IP rather than the new IP.  The process could be accelerated by doing one of two things:

  • Restarting the workstation
  • Running IPConfig /FlushDNS

 

The first is rather excessive, and the second used to require local administrator permissions.  This meant that a standard end-user had to use option #1.  Or wait.

Neither of these were good solutions.  Thankfully there is better news…

 

Old Windows Behaviour

When the /FlushDNS parameter was added back in Windows 2000 it required local administrator access to run the command.  This was true for many other things, such as setting the time zone.

The below shows the behaviour when running IPConfig /FlushDNS in  the original Windows 10 builds.  The below is build 10.0.10240 which is 1507 AKA Threshold 1.

Elevation Required To Run IPConfig /FlushDNS

Note that the command was blocked

Current Windows 10 Behaviour

In the recent Windows 10 builds, elevation is no longer required to run IPConfig /FlushDNS – yay!

Elevation No Longer Required To Run IPConfig /FlushDNS

 

Cheers,

Rhoderick

Rhoderick Milne [MSFT]

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