Truncated DNS message over UDP

Sebastiano Di Paola sebastiano.dipaola at
Wed Jun 27 08:43:17 UTC 2012

Hello everyone,
before sending this email I tried do some seaches on this topic, but
no luck so before bothering bind-workers here's my question

I was wondering if a configuration option exists in order to force
bind server to send a "minimal (from size and number of returned
record point of view)" response in case the trucated bit is set in the

Let me explain better...
1) Client asks for "" type ANY to my server (RD bit is set)
2) Server gets the response (does not matter if from cache or not) but
the answer is bigger than 512 bytes (or the server has  udp-max-size
512 parameter in configuration)
3) Server send answer with TC bit = 1, but instead of giving partial
response header is like this QDCOUNT = 1, ANCOUNT = 0, NSCOUTN = 0,
ADDITIONAL=0 (if there is no EDSN0 in query) and just sent back the
question section.
4) Client (if needed) re-do the query using TCP (some clients does not
use records contained in packets with TC bit set in the header)

If I'm not wrong RFCs does not state that partial answer must be
returned to the client, so probably there is no issue in getting rid
of them (with a configuration option :) )

Is there any parameter that could let me achieve this result?
Kind regards.

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