Upon upgrading the Linux Kernel version (usually in CentOS 4.6 – 5) you may get the following error when trying to start APF:
Unable to load iptables module (ipt_state), aborting.
To fix this, open /etc/apf/internals/functions.apf and locate the following lines:
ml ipt_state 1 ml ipt_multiport 1
And replace them with:
ml xt_state ml xt_multiport
Then restart APF.