Some functions of iptables does not working in a cpanel server

[mateusd24]

One of my server which have cpanel some rules of iptables is not working.

For example, when I use
Code:
- iptables -N syn_flood
- iptables -A INPUT -p tcp --syn -j syn_flood
- iptables -A syn_flood -m limit --limit 1/m --limit-burst 4 -j RETURN
- iptables -A syn_flood -j DROP

and I try to test, it do not show any good results, but when I try to use in a server which do not have cpanel this function works fine.
I have searched a bit and I found a old topic that the guy practically is having the same problem as me but he do not found a fix https://forums.cpanel.net/f5/my-server-under-syn-botnet-how-can-i-prevent-attack-147781.html
How do i solve this problem?

 

[cPanelMichael]

Hello

You mentioned those rules work well on another server without cPanel installed. Did you verify the server these rules work with is using the same OS, Kernel, and VPS environment (if it's a VPS)?

Thank you.

 

[mateusd24]

Hi,
Yes, I tried with 2 others servers, one of them have ubuntu(Ubuntu 12.04 x86_64) and the rules works and the other have the same OS (CentOS 6 64-bit) of my cpanel server and worked too, but in my cpanel server (CentOS 6 64-bit) wont worked. The only different thing is: the two servers with out cpanel is a VPS and the server with cpanel is a dedicated.

 

[cPanelMichael]

It seems like the issue is likely related to the OS/Kernel and not directly with cPanel. cPanel does not install firewall rules or manage the iptables firewall itself. Have you considered installing a firewall management utility such as CSF and adding the rules through that?

Thank you.

 

[mateusd24]

I have installed this cpanel plugin ConfigServer Security & Firewall but some functions doesn't worked like the "SYN Flood protection". I have tested again in other server with cpanel that I bought recently to test this problem (CentOS 6 x86_64) and the problem still persist on this new cpanel server. This is quite strange, as I'm seeing the cpanel server is blocking the use of some rules.

 

[cPanelMichael]

I don't suspect that cPanel itself is preventing you from using any particular iptables firewall rules. It sounds more like an issue with the OS/Kernel. You may want to post directly to the ConfigServer support forums if certain features of it are not working properly so they can troubleshoot the issue.

Thank you.

 

[mateusd24]

Ok, thanks