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Re: caching dns lookups



On Thu, Aug 30, 2001, Dan Kenigsberg wrote about "Re: caching dns lookups":
> Nadav, am I the only one seeing 'resolving foo.bar.com' in the status line for
> long seconds?

I was never troubled by such a problem. It can happen, however, when the modem
is busy downloading a long file (for example), when, as I said, the round-trip
time is as much as 2 seconds (try pinging your DNS server to see the round-trip
time to it).

Can you tell us a bit about your configuration -
are you connected to the Technion or a commercial ISP? What nameserver did
you use before switching to a local named?

> > This isn't too bad for casual web browsing and similar activity
> > (and note that individual applications do cache the DNS resolutions, so
> > Mozilla doesn't have to resolve the same domain name over and over).
> 
> So I really cannot explain why I sometimes get DNS errors messages
> when I click 'next' on a google page. 
> I'll have to tcpdump to the bottom of it.

Something is rotten in the kingdom of Denmark :)
Could it be that you're, say, connected to one ISP but using a faraway's
ISP's nameserver? Probably not. I know you know better then that :)

I just thought of a very important thing:

You seem to be only measuring resolve times in your browser. But if you're
using a (non-transparent) HTTP proxy, your browser actually has no business
resolving the domain name! It passes the unresolved domain name to the proxy,
and it is up to the proxy to resolve these domain names! So if this is the
case (e.g., if you're connected to the technion you *must* be using a proxy),
your name server cannot have anything to do with the speed of domain name
resolution on a web browser, and installing a local named won't make one
iota of difference - only fixing the name server on the proxy can make a
difference.

Can you please do timing on actual "nslookup" (or "host", "dig", or whatever
you prefer) commands, and see if it's really that bad without the local
named, and how it changes when you enable a local named? Try checking the
same domain several times, seeing if the second lookup is faster than the
first, or you always get these "long seconds" delay.


-- 
Nadav Har'El                        |      Thursday, Aug 30 2001, 11 Elul 5761
nyh@math.technion.ac.il             |-----------------------------------------
Phone: +972-53-245868, ICQ 13349191 |echo '[q]sa[ln0=aln256%Pln256/snlbx]
http://nadav.harel.org.il           |sb3135071790101768542287578439snlbxq'|dc

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