Re: system taking ages to resolve dns

[Florian Kulzer <florian.kulzer+debian@icfo.es>]

On Sun, Jul 05, 2009 at 17:25:24 -0500, Hugo Vanwoerkom wrote:
> Florian Kulzer wrote:

[...]

> >Do you see any difference in the response time for the following two
> >queries?
> >
> >dig -t A debian.org
> >
> >dig -t AAAA debian.org
> >
> 
> Florian, I get the following (edited) results:
> 
> hugo@debian:~$ dig -t AAAA debian.org Query time: 130 msec
> hugo@debian:~$ dig -t AAAA debian.org Query time: 127 msec
> hugo@debian:~$ dig -t AAAA debian.org Query time: 129 msec
> hugo@debian:~$ dig -t AAAA debian.org Query time: 147 msec
> hugo@debian:~$ dig -t AAAA debian.org Query time: 135 msec
> hugo@debian:~$ dig -t AAAA debian.org Query time: 129 msec
> hugo@debian:~$ dig -t AAAA debian.org Query time: 145 msec
>                                           average 134.5
> hugo@debian:~$ dig -t A debian.org Query time: 151 msec
> hugo@debian:~$ dig -t A debian.org Query time: 177 msec
> hugo@debian:~$ dig -t A debian.org Query time: 150 msec
> hugo@debian:~$ dig -t A debian.org Query time: 152 msec
>                                        average 157.5
> 
> so dig -t AAAA debian.org is on the average 157.5-134.5=23 ms faster.
> 
> What does that mean?

Try "host -t AAAA debian.org"; I get this response "debian.org has no
AAAA record". If this reaction is fast then everything is alright
because your system will immediately send an IPv4 query after such a
reaction. Problems arise only if broken nameservers simply ignore the
initial AAAA query so that it has to time out before the system fall
back onto the IPv4 query.

I do not know why your nameserver is consistently faster for the
unsuccessful IPv6 queries; this probably depends on its configuration.
Maybe it simply rejects all IPv6 queries right away without even trying.

-- 
Regards,            | http://users.icfo.es/Florian.Kulzer
          Florian   |