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I'm trying to implement dns service discovery in my application (no, I'm not asking for a programmatic answer). What I believe is one of my big pain points is generating the query. I know I need to send out a multicast broadcast on port 5353 and want to look for devices of type _ipp._tcp and _print._tcp, but I don't know what the question section needs to look like.

For example, in SSDP I sent out a query that looks like the following:

"M-SEARCH * HTTP/1.1\r\n"
"HOST: 239.255.255.250:1900\r\n" +
"MAN: \"ssdp:discover\"\r\n"
"ST: urn:schemas-upnp-org:device:Printer:1\r\n"
"MX: 5000\r\n\r\n"

From what I know about a DNS query I need to send something like:

"_ipp.tcp,all,all"

but I know there needs to be more.

Any pointers to documentation, etc would be greatly appreciated!

update rfc1035 appears to contain promising information re the message structure.

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Between rfc1035 and wireshark, I have a pretty decent picture of what a query looks like. For a standard query, basically the Answer/Authority/Additional fields will be blank. The header contains general information including how many Question sections are included.

+---------------------+
|        Header       |
+---------------------+
|       Question      | the question for the name server
+---------------------+
|        Answer       | RRs answering the question
+---------------------+
|      Authority      | RRs pointing toward an authority
+---------------------+
|      Additional     | RRs holding additional information
+---------------------+

Wireshark even gives you the bits and hex view of the DNS query. It's a pretty cool tool that I wish I knew about sooner.

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