Date: Fri, 9 Jan 2004 23:08:01 +0000 From: Jez Hancock <jez.hancock@munk.nu> To: Alexandre Krasnov <tech@tern.ru> Cc: freebsd-security@freebsd.org Subject: Re: Problem with DNS (UDP) queries Message-ID: <20040109230801.GE1488@users.munk.nu> In-Reply-To: <1839710842.20040109181325@tern.ru> References: <1775511953.20040109173220@tern.ru> <20040109144956.GB87284@users.munk.nu> <1839710842.20040109181325@tern.ru>
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On Fri, Jan 09, 2004 at 06:13:25PM +0300, freebsd@tern.ru wrote: > Yes, I had thought about what you wrote. > Because of this I mentioned that 'I do not want to turn off the "log > in vain" feature.' In that case I imagine you'd need to hack the kernel source code to make it not log vain udp port 53 requests. I'm fairly sure it's an 'all or nothing' sysctl mib/flag. Why do you want to log those vain connection attempts using 'log_in_vain' though? It would be a lot more suitable to use the logging feature in ipfw2 and disable the log_in_vain feature completely. Just my opinion though :P > JH> On Fri, Jan 09, 2004 at 05:32:20PM +0300, freebsd@tern.ru wrote: > >> Hi all > >> > >> I am trying to get rid of strings: > >> kernel: Connection attempt to UDP FREEBSD_IP:port from DNSSERVER_IP:53 > >> on my console and in log file > >> > >> I understand that those are replies on DNS queries that for some reason > >> took too long time to be answered. > >> I do not want to turn off the "log in vain" feature. > >> > >> As these strings fill up my log I am afraid to miss some sensitive > >> messages (e.g. hacker's attack :) > >> > >> I'm using FreeBSD 5.1 with ipfw2 that allows via static rules both > >> DNS queries and DNS replies. > >> > >> The main application that generates queries is sendmail. > >> > >> What can be done? > JH> I believe those messages are generated if the following sysctl flag is > JH> set: > > JH> net.inet.udp.log_in_vain > > JH> you can disable it by executing: > > JH> sysctl net.inet.udp.log_in_vain=0 > > JH> on the commandline. > > JH> Obviously though this will disable logging of all vain connection attempts using > JH> the udp protocol. However if you have ipfw set up to log such attempts, > JH> you don't really need that sysctl flag set anyway. > > JH> See also the tcp equivalant flag: > > JH> net.inet.tcp.log_in_vain > > JH> also see the manpage for rc.conf(5) regarding the log_in_vain rc.conf > JH> setting. > > Alex. > > -- Jez Hancock - System Administrator / PHP Developer http://munk.nu/ http://jez.hancock-family.com/ - personal weblog http://ipfwstats.sf.net/ - ipfw peruser traffic logging
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