Problem resolving one particular domain

Stephane Bortzmeyer bortzmeyer at
Wed Jul 27 08:31:30 UTC 2011

On Wed, Jul 27, 2011 at 09:59:32AM +0200,
 Danilo Godec <danilo.godec at> wrote 
 a message of 247 lines which said:

> Weirdness number 2 - using dig directly with their servers works:

Nothing weird here: dig does not behave like the BIND resolver. It
does not use EDNS at all by default, it does not use the same source
port, etc.

> >09:53:23.643138 > [udp sum ok]
> >7984 [1au] A? ar: . OPT UDPsize=512 (43) (ttl 63,
> >id 5640, len 71)

There is one weird thing here: your resolver uses always the same
source port, 53:

1) It means you are vulnerable to Kaminsky-style cache poisoning. In
2011, 'query-source port 53;' should have disappeared a long time
ago. Source ports must be random.

2) It may create problems with some firewalls (this would not explain
why, on the same servers, work).

A second weird thing is the use of EDNS with a buffer size of
512. This is completely useless, since default size is already 512
(but it is probably not the cause of the problem since all answers
from Rabobank are short).

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