[avahi] PTR query responses

Markus Rathgeb maggu2810 at googlemail.com
Mon Mar 12 09:25:41 PDT 2012

2012/3/12 Christiano F. Haesbaert <haesbaert at haesbaert.org>:
> On 12 March 2012 13:08, Markus Rathgeb <maggu2810 at googlemail.com> wrote:
>> Hello!
>> I have here multiple machines with the same setup.
>> Normally if a multicast question for a PTR "_srv._proto.local" is
>> made, the machines reply with a multicast response containing four
>> records, the types PTR, TXT, SRV, A.
>> This morning I see (wireshark) a machine that reply contains only the
>> PTR record -- missing the TXT, SRV and A type.
>> If a multicast question for the A record of the machine's name is
>> requested, the machine answered with a multicast respone given the A
>> record.
>> After a restart of the avahi daemon of this machine, the machine's
>> reply to the PTR question contains all four records (PTR, TXT, SRV, A)
>> again.
>> What's going on?
>> Could someone explain me, how I could run in that situation and
>> whether it is correct or not (why)?
>> Thanks in advance,
>> Markus
> There is a feature called something like "Known Answer Suppression",
> the querierer includes the known answers in the query packet, under
> the AN section, so the the one getting queried won't include the known
> answers in the reply.
> Not sure if I made myself clear, try using avahi-browse, if the
> service ain't there, it's wrong.
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Thank you for the reply.

avahi-browse shows the service.
avahi-resolve-hostname could resolve the A record.

The windows command line tool dns-sd seems also to be working (-B and
-G v4 hostname).

I got the error with some tools written by colleagues.
So I do not say it is an error of avahi (it could be an error in the
implementation of the tools).

The mutlicast PTR question for the special service is done to get a
list of all machines that are offering that service (no "known answer"
So it is possible to request the A record for every machine that sends
an answer and no A record in the answer was included.

The question is: Why are always the four record types in the answer
and now one machine replies with only one record type in the answer (I
never seen this before and after restart of avahi I see four record
types again for this machine)?
The restart of avahi was done after about four hours.

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