Configuring different TTLs in multiple RRs for the same domain name, TYPE, and CLASS

Dave Warren davew at
Fri Mar 25 20:15:13 UTC 2016

On 2016-03-25 07:21, Barry Margolin wrote:
> In article <mailman.456.1458889802.73610.bind-users at>,
>   Dave Warren <davew at> wrote:
>> I'm more interested in the impact from the perspective of an
>> authoritative server operator and in some respects sites that use short
>> TTLs will increase the odds of my longer-TTL's records staying in the
>> cache longer before it gets hit by a cache-size limit, but none of my
>> zones are really large enough to do A/B testing.
> IMHO, memory is so cheap these days that any server that has to eject
> cache entries because of memory limits means the server operator isn't
> really trying to do their job well.

If you're running a dedicated public/ISP/massive-corporation resolver, 
sure, this is true. But if your resolver is some random DNS server on a 
small corporate Active Directory and one of dozens of services on a 
$1000 server with 1-50 users, who cares if your DNS cache only carries 5 
minutes, 30 minutes, or 6 hours of cache?

In fact, if your resolver just forwards queries to your ISP, and your 
ISP has dedicated caches, there would be very little measurable 
difference at all. I'm not a fan of forwarding, but many admins set it 
up because it's there without considering whether it's needed or not.

Dave Warren

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