Re: [Exim] Caching DNS and Exim

> michael@??? probably said:
> > I noticed a large performance gain back then when I installed a caching
> > name server. I advise you not to use forwarders, which avoids problems
> > with locally screwed up delegations, if there are any.
>
> Being part of our networking group and the person who runs the local
> name servers, I cringe when I see advice like that. It's exactly
> what I _don't_ want people to do.

All your arguments are correct, but I think I should elaborate. I am
not against cache hierachies, but I advise not to use a DNS server with
local domains as forwarder. If domains move to new name servers, using
a forwarder to the local server will still resolve the old zone. Using a
cache that resolves via root name servers will use the correct zone ASAP
which is usually earlier than when your hostmaster changes named.conf.

> If you don't care about bandwidth and if you don't care about your
> machine thrashing if it's performance is already borderline, you don't
> care about performance gains from other local caches and you don't
> care about allowing other people to benifit from that cached
> information.

Honestly, with 16 GB mail traffic a day, I doubt the extra lookups cost
me much bandwidth. Further, it takes a much longer time to detect that
a remote name server that you use as forwarder is down. That happens
only rarely, but it can kill a busy system.

So the answer probably is: It depends if a local DNS cache is useful.
There is more to think about than just resource usage.

Michael