How does DIG utility work in FreeBSD and BIND?

user_3552519 0
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I want to know how does the DIG (Domain Information Groper) command really works when it comes to code and implementation. I mean when we enter a DIG command, which part of the code in FreeBSD or BIND hits first.

Currently, I see that when I hit the DIG command, I see the control going to a file client.c. Inside this file, following function is called:

static void client_request(isc_task_t *task, isc_event_t *event);

But how does the control reach to this place is still a big mystery for me even after digging a lot into 'named' part of the BIND code.

Further, I see this function being called from two places within this file. I tried to put logs into such places to know if control reaches to this place through those paths, but unfortunately that doesn't happen. It seems "Client_request()" function is somehow being called from outside somewhere that I am not able to figure out.

Is there anybody here who can help me out to resolve this mystery for me ?

Thanks.

named dig bind dns freebsd
2 Answers

Not only for bind but to any other command, within FreeBSD you could use ktrace, it is very verbose but could help you to get a quick overview of how the program is behaving.

For example, in latest FreeBSD's you have drill command instead of dig so if you would like to know what is happening behind scenes when you run the command, you could give a try to:

# ktrace drill freebsd.org

Then to disable tracing:

# ktrace -C

Once tracing is enabled on a process, trace data will be logged until either the process exits or the trace point is cleared. A traced process can generate enormous amounts of log data quickly; It is strongly suggested that users memorize how to disable tracing before attempting to trace a process.

After running ktrace drill freebsd.org a file ktrace.out should be created the one you could read with kdump, for example:

# kdump -f ktrace.out | less

That will hopefully "reveal the mystery", in your case, just replace drill with dig and then use something like:

# ktrace dig freebsd.org
user_11354240

Thanks to FreeBSD Ports system you can compile your own BIND with debugging enabled. To do so run

cd /usr/ports/dns/bind913/ && make install clean WITH_DEBUG=1

Then you can run it inside debugger (lldb /usr/local/bin/dig), break on the line you are interested in and then look at backtrace to figure out how the control reached there.

user_6376690
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