Some domains don't resolve.

Barry Margolin barmar at
Tue Jun 10 00:30:15 UTC 2008

In article <g2i9hm$2m2u$1 at>, Danny Mayer <mayer at> 

> Barry Margolin wrote:
> > In article <g2aeee$1bb9$1 at>, Kevin Darcy <kcd at> 
> > 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.
> > 
> I wonder how many people remember HTTP Caching Servers? They have fallen 
> out of use in most places because there was almost no benefit to using 
> them. DNS is much the same when it comes to forwarders. Don't forget 
> that DNS already does caching, it's intrinsic to DNS.

There's so much dynamic content, or advertising content that wants to 
track the number of users accessing it, that caching web sites is pretty 

DNS is much more cacheable, so I don't think the problems with web 
caches can be extended to DNS caches.

Barry Margolin, barmar at
Arlington, MA
*** PLEASE don't copy me on replies, I'll read them in the group ***

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