How to fix “nf_conntrack: table full, dropping packet.” issue
during high traffic time, web site become much slower while low traffic is ok. a typical case is a download server, when there are many concurrent connections to download, many or all users feel much slower. one cause may be the linux conntrack table is full.
Check
#dmesg | tail nf_conntrack: table full, dropping packet. nf_conntrack: table full, dropping packet. nf_conntrack: table full, dropping packet.
if you see above, then the issue of conntrack table full is confirmed.
#sysctl -a | grep conntrack ... net.netfilter.nf_conntrack_max = 65536 net.netfilter.nf_conntrack_count = 68999 net.netfilter.nf_conntrack_buckets = 16384 ... #cat /sys/module/nf_conntrack/parameters/hashsize 16384
if nf_conntrack_count is close to nf_conntrack_max or even larger, the problem will occur.
Action
#sysctl -w net.netfilter.nf_conntrack_max=655360 net.netfilter.nf_conntrack_max = 655360 #echo 163840 > /sys/module/nf_conntrack/parameters/hashsize
Permanent Change
edit /etc/sysctl.conf, add following line:
net.netfilter.nf_conntrack_max=655360
edit /etc/rc.local, add following line:
echo 163840 > /sys/module/nf_conntrack/parameters/hashsize