I have several Xen and KVM vps servers and they all suffer with the same problem of “nf_conntrack: table full, dropping packet” but its an easy fix
You can check what the current number of nf_conntrack_max is set to.
the default is 65535 but all mine were set to 15000.
Now to increase the number of nf_conntrack_max
echo 100000 > /proc/sys/net/nf_conntrack_max
Now if you check again it should be the new value.
Now to make the change permanent we add the following to the bottom of /etc/sysctl.conf
net.nf_conntrack_max = 100000
Please note that the directory path to “nf_conntrack_max” differs between Linux distributions, the above works for CentOS