35

How often does the DNS cache clear on a Windows 7 machine?

Improve this question

3 Answers 3

Reset to default
39

The DNS cache doesn't ever flush, unless you explicitly tell it to or you make a DNS/networking related configuration change. DNS records have a Time To Live (TTL) value associated with them which tells a DNS cache how long the particular record is good for. Records in the cache are kept for their TTL, then re-queried.

On a Windows machine you can see a list of all the records in your cache along with their TTL by executing the following command at the command prompt:

ipconfig /displaydns

You can force a flush of all cached DNS records using the following command:

ipconfig /flushdns

For more info:

Improve this answer
3
  • 1
    What kind of things constitute a "networking change"? A new IP address, joining a different wifi network? or manually flushing the cache / setting DNS
    – cutrightjm
    Feb 27, 2015 at 1:01
  • 2
    According to the other answers (and common sense), it appears like there is indeed a maximum lifetime for cached DNS entries in Windows. Consider the opposite: It would then be trivial for websites to perform a denial-of-service attack against visitors by triggering a huge number of DNS queries over time, until Windows runs out of HDD/RAM/CPU because of the ever-increasing cache size. So this answer seems wrong.
    – Zero3
    Mar 19, 2017 at 1:07
  • @Zero3 That can be explained via a per-entry TTL (which may have a maximum value such that no entry is held over this time; the answer does not claim that there cannot be a maximum TTL). Thus the answer can be true, in it's assertion that there is no "[entire] cache flush", while still explaining the counter-argument behavior because entries are "flushed" (expired) individually by their own TTL entries .. granted, a little bit of wording cleanup might help.
    – user2864740
    Jun 14, 2018 at 22:53
12

From what I've been able to find, Windows 7 does not set a parameter for dnscache MaxCacheEntryTtlLimit.

The default value for MaxCacheEntryTtlLimit is DWORD = 0x15180 = 86400 seconds = 1 day

  • if DNS zone TTL < MaxCacheEntryTtlLimit, then DNS TTL is used
  • if DNS zone TTL > MaxCacheEntryTtlLimit, then MaxCacheEntryTtlLimit is used
Improve this answer
8

According to: Reduce DNS Client Cache in Windows Server 2012 R2

Instead of MaxCacheEntryTtlLimit you should modify maxcacheTTL. It works for Windows 8 too.

Description

Determines how long the Domain Name System (DNS) server can save a record of a recursive name query.

If the value of this entry is 0x0, the DNS server does not save any records.

enter image description here

Improve this answer
2
  • Thanks! Exactly what I was looking for. One more thing to add from that blog post run net stop dnscache & net start dnscache to make setting take without rebooting.
    – Lucas
    Jul 11, 2014 at 9:50
  • 1
    For what it looks like, maxcacheTTL is for the "DNS server" component of Windows Server, not for the DNS Cache.
    – Jeroen Landheer
    Aug 7, 2015 at 7:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.