[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: caching dns lookups
- To: "Nadav Har'El" <nyh(at-nospam)math.technion.ac.il>
- Subject: Re: caching dns lookups
- From: Tzafrir Cohen <tzafrir(at-nospam)technion.ac.il>
- Date: Thu, 30 Aug 2001 18:08:46 +0300 (IDT)
- Cc: Dan Kenigsberg <danken(at-nospam)cs.technion.ac.il>, <linux-il(at-nospam)linux.org.il>
- Delivered-To: linux.org.il-linux-il@linux.org.il
- In-Reply-To: <20010830150931.A435@leeor.math.technion.ac.il>
- Sender: linux-il-bounce(at-nospam)cs.huji.ac.il
On Thu, 30 Aug 2001, Nadav Har'El wrote:
> 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 theTechnion 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
> > > Mozilladoesn'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 thisis 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.
Yes, it does.
wget http://www.technion.ac.il/proxy.pac and see exactly what netscape
checks before even contacting the proxy.
Netscape should have a seperate process for DNS lookups, IIRC.
>
> 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.
--
Tzafrir Cohen
mailto:tzafrir@technion.ac.il
http://www.technion.ac.il/~tzafrir
=================================================================
To unsubscribe, send mail to linux-il-request@linux.org.il with
the word "unsubscribe" in the message body, e.g., run the command
echo unsubscribe | mail linux-il-request@linux.org.il