Some domains don't resolve.
barmar at alum.mit.edu
Sat Jun 7 14:53:23 UTC 2008
In article <g2dhd2$1mb8$1 at sf1.isc.org>,
Sten Carlsen <ccc2716 at vip.cybercity.dk> wrote:
> The question as I read it, is if a very small amount of users will
> benefit most from using the cached lookups of a large number of users
> (the whole ISP population) or from having their own independent resolver.
> I have that situation here, I first used forward but later switched to
> just resolving. My feeling (I have no statistics) is clearly in favour
> of NOT forwarding. I don't see any speed penalty in real life but got
> rid of some mysterious issues that happened while forwarding and the
> speed seems to be higher.
I'm not saying that I recommend forwarding. I don't, because it adds an
extra layer of dependency, and the benefit is probably not worth it.
I was just refuting the guy who said that the theory that you get better
cache hits is a myth.
> Barry Margolin wrote:
> > In article <g2aeee$1bb9$1 at sf1.isc.org>, Kevin Darcy <kcd at chrysler.com>
> > wrote:
> >> Barry Margolin wrote:
> >>> But if your ISP has 100,000 users of the same caching server, it will be
> >>> cached if any of 1,000 users have accessed it recently. For any one of
> >>> them, there's only a 0.1% chance that their lookup will be the one that
> >>> has to wait for fetching from the source.
> >> And if you have 100,000 users using the same caching server, it's likely
> >> to experience big spikes of activity (e.g. several thousands of queries,
> >> within the course of less than a second), during which time some users
> >> will experience some extra delay in getting their queries resolved.
> > Certainly if the nameserver is not engineered to handle the load it's a
> > bad idea to use it as a forwarder. That's a completely different issue
> > than whether it's useful to share caches via a forwarding hierarchy.
Barry Margolin, barmar at alum.mit.edu
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