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

Barry Margolin barmar at
Sat Mar 26 02:15:38 UTC 2016

In article <mailman.469.1458936922.73610.bind-users at>,
 Dave Warren <davew at> wrote:

> 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.

If you're running a resolver for a small organization, the cache isn't 
going to get huge in the first place. How many different names will 50 
users access in a day?

Barry Margolin
Arlington, MA

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