A courtesy flush of the dns cache please …..

Windows dns cache is there to allow the results of dns lookups to be stored. When a Windows XP or Windows 2000 machine queries a DNS server, the response is either positive (a match was found) or negative (no match was found). The OS stores these results in a local DNS cache so that local clients don’t repeatedly query the DNS server for the same address. These DNS cache entries are known as DNS resource records, and the DNS resolver always checks the local cache before it queries the DNS server.

It can be very beneficial to check the entries in the dns cache to see what results are being stored – for example I found a machine which was having problems accessing shares across a vpn and the cache showed that the client was patently not able to connect to the domain controller that was supposed to authenticate it !!!

To see the contents of the cache and its ttl (time to live values) use the command ipconfig /displaydns



Record Name . . . . . : www.mac.com

Record Type . . . . . : 1

Time To Live . . . . : 5008

Data Length . . . . . : 4

Section . . . . . . . : Answer

A (Host) Record . . . :

If you wished to have the cache cleared to see what the current lookup operations would generate.

It was during an ipconfig /flushdns command that a message “Could not flush the DNS Resolver Cache: Function failed during execution” appeared. The client tried logging on as a domain admin to clear this but was still unsuccessful.

The solution – a third party application used for storing various settings to allow portables to be used at various locations with differing IP addresses. The problem is that the dns client service is disabled. So to correct this then go into control panel / services and change the properties on this service to be manual or automatic startup and then start it. Once started refresh the cache with the ipconfig /flushdns and ensure it completes successfully.

Happy Flushing !!