Efficacy of using short timeout values for an A record

Chris Buxton chris.p.buxton at gmail.com
Tue Feb 14 19:32:45 UTC 2012

On Feb 14, 2012, at 11:23 AM, Chuck Swiger wrote:
On Feb 14, 2012, at 11:11 AM, Alan Clegg wrote:
>> On 2/14/2012 1:42 PM, Chuck Swiger wrote:
>>> ISC's BIND has (or had) a MINTTL value of 5 minutes / 300 seconds.
>>> It's probably unreasonable to expect other platforms to refetch DNS
>>> records faster than that.
>> Uh... no.  BIND has always respected TTL when caching information.
> See http://www.ietf.org/rfc/rfc1035.txt
> "The MINIMUM value in the SOA should be used to set a floor on the TTL of
> data distributed from a zone.

The original question is from the standpoint of the recursive server, not the authoritative server.

Yes, BIND 4 imposed a minimum value, but only on authoritative data. Not on cached data.

BIND has (or perhaps had) the ability to impose a minimum TTL on cached data, but most implementations do not enable this. As I recall, the value has to be set in the source code before compiling the binary.

Chris Buxton
BlueCat Networks

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