Interesting thing with DNS requests

[Thiago Macieira]

Fredrik Johansson wrote:
>torsdag 07 december 2006 04:26 skrev Pavel Troller:
>> > How is requiring 15x as much data to do the same thing not a bug?
>> > Both apps running in the same environment implies that this has
>> > nothing to with the DNS server performance--the konqueror client
>> > must be issuing far more DNS requests than the Firefox client.

It is not a bug. The slowness you're experiencing is not caused by the 
extra DNS round-trips.

For whatever reason, kio_http isn't keeping those connections alive, so 
it's connecting way more often. And for each connect, there's DNS lookups 
(plural). There is a bug in glibc that causes extra, unnecessary lookups, 
though. Feel free to report it.

>> Hi!
>>   Isn't it because KDE is by default trying IPv6 first when it detects
>> that the machine is IPv6 enabled ? From my experiences, many DNSs
>> still behave incorrectly on IPv6 (like AAAA or similar) queries so the
>> additional traffic may be caused by this. Try to use tcpdump or
>> wireshark to find, what your machine tries to query from the DNS.

It isn't the case here. The symptom of broken IPv6 replies are things not 
being found or timing out, instead of taking long to render a page.

>Also if that is the case shouldn't it try IPv6 once and if it fails go
> for plain IP for future requests?

It does. DNS works perfectly in that aspect. The nameserver caches the 
reply, but unfortunately it doesn't cache a no-reply for a field. I don't 
know if nscd does.

But, for the same reason we look up again, we don't cache anything in the 
KDE Libraries: we (I) simply don't want to implement DNS rules in KDE. 
You have daemons that do that way better than we could. So use them.

-- 
  Thiago Macieira  -  thiago (AT) macieira.info - thiago (AT) kde.org
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