![]() To make this not happen, check and decrease the other nf_conntrack timeout connection tracking values: linux:~# sysctl -a | grep conntrack | grep timeout Therefore, for large flows of traffic even if you increase nf_conntrack_max, still shorty you can get a nf_conntrack overflow table resulting in dropping server connections. Generally, the default value for nf_conntrack_* time-outs are (unnecessery) large. Decreasing other nf_conntrack NAT time-out values to prevent server against DoS attacks al nf_log/ total 0 dr-xr-xr-x 0 root root 0 Mar 23 23:02. There you can find some values dynamically stored which gives info concerning nf_conntrack operations in "real time": linux:~# cd /proc/sys/net/netfilter linux:/proc/sys/net/netfilter# ls proc/sys/net/netfilter kernel memory stored directory. ![]() – For the diagnosis of nf_conntrack stuff there is Note: Be careful with this variable, according to my experience raising it to too high value (especially on XEN patched kernels) could freeze the system.Īlso raising the value to a too high number can freeze a regular Linux server running on old hardware. – To permanently store the made changes a) put into /etc/nf: linux:~# echo '_conntrack_count = 131072' > /etc/nfī) put in /etc/rc.local (before the exit 0 line): echo 32768 > /sys/module/nf_conntrack/parameters/hashsize The rule to calculate the right value to set is: hashsize = nf_conntrack_max / 4 linux:~# echo 32768 > /sys/module/nf_conntrack/parameters/hashsize The Hash table hashsize value, which stores lists of conntrack-entries should be increased propertionally, whenever _conntrack_max is raised. – Increasing the size of nf_conntrack hash-table However on many not so heavily traffic loaded servers just raising the _conntrack_max=131072 to a high enough value will be enough to resolve the hassle. I say temporary, because raising the nf_conntrack_max doesn't guarantee, things will get smoothly from now on. One temporary, fix if you need to keep your iptables NAT rules is: linux:~# sysctl -w _conntrack_max=131072 I would suggest also setting your firewall rules to reject rather than drop
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