how often does the DNS cache clear?

Question

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

Answer 1

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:

• Wikipedia article on DNS and TTLs

Answer 2

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