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Understanding DNS TTL Record

Posted on 2016-08-28
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Last Modified: 2016-08-29
Let's say we have a DNS zone with TTL of 24 hours, then I want to change it to 1 hour.
Will the PCs wait 24 hours to update their DNS cache (TTL) to 1 hour ? assuming they are not rebooted, and DNS has not been manually refreshed.

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Question by:jskfan
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Bing CISM / CISSP earned 280 total points
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you no need to wait for that long. you may manually flush the existing DNS cache on a computer using the following command lines:

Windows: IPCONFIG /FLUSHDNS

OS X: dscacheutil -flushcache

Linux: /etc/rc.d/init.d/nscd restart
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by:davorin
davorin earned 220 total points
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If you don't refresh dns manually, then you need to wait for 24 hrs (or TTL time specified before the change.)
PC  checks the dns record, gets the value and sees that it is valid for 24 hrs (firstly specified TTL time), so for the next 24 hrs it is not checking DNS server for changes. Within 24 hrs you change TTL to 1 hr. So after 24 hrs the PC is checking for DNS changes every 1 hr.
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by:jskfan
ID: 41775078
Thank you Guys
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