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Date:      Wed, 05 Jun 2013 07:24:48 -0500
From:      "Mark Felder" <feld@feld.me>
To:        freebsd-questions@freebsd.org
Subject:   Re: System Calls that do DNS
Message-ID:  <op.wx7grmqv34t2sn@markf.office.supranet.net>
In-Reply-To: <F5EBDC53-CBA3-415D-B7CD-1EC873692348@lafn.org>
References:  <F5EBDC53-CBA3-415D-B7CD-1EC873692348@lafn.org>

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On Mon, 03 Jun 2013 21:57:07 -0500, Doug Hardie <bc979@lafn.org> wrote:

> I have an unusual situation.  A program is doing a DNS lookup and often  
> the IP address has no reverse DNS entries.  As a result the program  
> hangs for several timeouts.  The call is not being made directly in its  
> code, but is occurring in a system call.  There are no specific calls to  
> DNS, its something else doing it.  I have been trying to track down  
> which system call is doing it, but without success so far.  I have tried  
> syslog calls around each of the system calls I thought might be the  
> culprit, but my guessing is not very good.  How can I identify the  
> system call that is calling DNS?  If I can find it, I hopefully can find  
> another way to do whatever it does that does not involve a reverse DNS  
> lookup.
>
>

The system DNS lookups are handled by libc. Probably somewhere in the code  
here:

http://svnweb.freebsd.org/base/head/lib/libc/nameser/



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