Hi. In am trying to write a simple program that send a udp datagram to a dns server and then gets the response. The problem is, I don't know how to create that datagram, and I don't know what message to send to the server. If it could only be as easy as with http (GET etc). Also, please note I am not simply trying to resolve names (I would have used gethostbyname() ), I must send a raw UDP datagram.

Places you should look:
1. For information on the mechanics of sending and receiving TCP/IP streams and datagrams, Beej's Guide.

2. For information regarding DNS, the internet RFCs related to DNS.

What I would do as part of the background research, set up a network sniffer to capture packets to and from a DNS server. Create a controlled DNS query using ordinary commands (like ping, for instance), capture the resulting exchange, and analyze that. Perhaps even set up something like netcat, configure a system to send DNS queries to it, and capture the results.

I sense that you are not telling us what your real intentions are. Perhaps with more information, someone can point out a simple and easy solution. Unless this is homework....

--- rod.

Thanks.

Actually I have read beej's guide a long time ago. Obviously, I know how to send datagrams (but this is not thanks to beej's guide but thanks to some books about sockets programming).

The problem is that constructing the dns header and the dns query by hand is quite unpleasant. I am not hiding anything, that's exactly what I want to do, send a raw udp packet and print back what the server sends.

You may be interested in the way gethostbyname does it. Download libc sources, unpack it and look into it's net directory. The whole query generation and response parsing is present.

DNS is actually a pretty straightforward protocol. RFC 1035 is what you really want to read. If your just looking to construct a single type of DNS request and handle the reply, you shouldn't have to spend too much time w/ it either.

Thank you for your replies. Of course I have already read the rfc . I have, in the end, read some gethostbyname source and decided to write the damn thing by hand. And actually I have to be able to construct all kinds of dns queries.. Anyway, thank you for your help.