[CentOS] ip_conntrack table filling up, dropping packets

yossarian1 at gmail.com yossarian1 at gmail.com
Tue Jun 12 11:42:17 UTC 2007

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.


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