2009/10/22 <exarkun@twistedmatrix.com>

On 20 Oct, 07:50 pm, jesper@taxboel.dk wrote:
>Hi Guys,
>
>Im playing with a dns-cache script, that overrides DNS requests for
>certain
>IP addresses.
>
>I would like to add functionality, so unresolved requests are sent to a
>spicific IP. How do I go about doing that?
>
>Is there a negative answer in the (udp) DNS protocol or am I forced to
>use a
>timeout.

You've overridden writeMessage to inspect messages for answers and
rewrite them if necessary. You can recognize error responses by looking
at the rCode attribute of the message object itself. This will take on
a value like dns.OK, dns.EFORMAT, dns.ESERVER, dns.ENAME, dns.ENOTIMP,
or dns.EREFUSED. You can handle these errors by making a request of
another domain, although since writeMessage is a very low-level API in
the process and not really intended to be overridden, I'm not sure how
you'll insert the responses you get from these new requests into the
original request/response process.

Jean-Paul

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