When you install Dome9 on a server that has CSF http://configserver.com/cp/csf.html installed, you can see that your CSF warns you that it is down.
CSF is a firewall configuration utility that helps you manually configure many features in your Linux iptables firewall - However, with Dome9 you don't have to worry again about configuring your servers. All you need to do is to set the security policy and Dome9 does the rest.
Since Dome9 provides very strong anti-brute-force protection, by eliminating it altogether as the ports are closed, many of the features offered by CSF are less relevant.
We recommend that you turn CSF off. This would help avoid false warnings from the CSF. You could leave it running but note that Dome9's anti tampering mechanism will override its settings.