[CentOS] ip_conntrack table filling up, dropping packets

Michael Calizo mike.calizo at gmail.com
Fri Jun 15 21:14:32 UTC 2007

Hi Michelson, I have that problem also on one of my FW box. What i did is i
created a cronjob that reload the iptables rule. In this case you dont drop
any connections and you dont need to reboot your box. So far its working on
our production deployed FW.

Note: You need to find out how frequent you do this on a weeks.


On 6/12/07, yossarian1 at gmail.com <yossarian1 at gmail.com> wrote:
> Hi, my ip_conntrack table is filling up and now my server is dropping
> packets. I'm running CentOS release 4.4 (Final) on a fairly busy
> webserver.  The table is full of various connections, including a lot
> of "ESTABLISHED" tcp connections from my webserver (the src is my
> webserver ip), and some other random connections to my webserver, and
> many "ASSURED" connections.  So why is it filling up? I changed the
> default timeout value like so:
> echo 36000 >
> /proc/sys/net/ipv4/netfilter/ip_conntrack_tcp_timeout_established
> but I don't think that's had any effect. any thoughts? what additional
> info can I provide that would be helpful?    I did find a script that
> clears out some of the stale connections using hping2, but I don't
> know if that's really a great solution to this problem.
> cat  /proc/sys/net/ipv4/ip_conntrack_max     # 34576
> after cleaning out the ip_conntrack table using an hping2 script:
> cat /proc/net/ip_conntrack | wc -l         # 3702     --  this number
> was around 34000 before I cleared it out because it was dropping
> packets. rebooting the machine, of course, clears it out.
> I've spent many hours banging my head against the wall trying to
> figure this out, reading in google groups and in various forums, to no
> avail.   My webserver does send out emails to a few thousand
> registered users (if they opt it for the email) every day.
> Thank you for your time!  I hope I sent this to the right list.  This
> looked like the right one.  Sorry in advance if I made a mistake.
> Michelson
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Mike Calizo
Registered Linux User # 365113

Even the longest journey has to start with a small first-step
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