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cPHulk Can’t Clear Blocks due to ip6tables | Demystified

by | Nov 24, 2021

cPHulk Can’t Clear Blocks due to ip6tables giving you trouble?

At Bobcares, we offer solutions for every query, big and small, as a part of our Server Management Service.

Let’s take a look at how our Support Team recently helped a customer when their cPHulk could not clear blocks.

Why cPHulk can’t clear blocks due to ip6tables

Have you been encountering problems when clearing cPHulk blocks? This often occurs if the iPv6 is disabled, broken, or not supported by the kernel. For instance, here is an example of the error:

[iptables] /sbin/ip6tables --list-rules cphulk failed: ip6tables v1.4.7: 
can't initialize ip6tables table `filter': Address family not supported by protocol 
Perhaps ip6tables or your kernel needs to be upgraded. : 
The subprocess reported error number 3 when it ended. 
at /usr/local/cpanel/Cpanel/ line 416.

cPHulk can be described as a security feature in cPanel that offers protection against brute force attacks. In fact, it locks down access to services as soon as it detects too many failed login attempts from a single IP address.

How to fix cPHulk can’t clear blocks due to ip6tables

  1. First, we need to run this command in case the iPv6 configuration is broken on the server:
    touch /var/cpanel/dns_flags/has_broken_ipv6
  2. Next, we will check if the kernel needs updating with the following command:
    yum check-update kernel

    In case an update is available, we can update the kernel via this command:

    yum update kernel

    Then, we will reboot the server in order to complete the kernel update.

  3. In some cases, Ipv6 may not be enabled yet on the server. In this scenario, we will have to contact the system administrator or hosting provider.

[Need further help? We are available 24/7.]


To sum up, the skilled Support Engineers at Bobcares demonstrated how to deal with cPHulk when it can’t clear blocks.


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