How To Disable The IPv6 on CentOS 6 with cPanel

IPv6 has been enabled on CentOS 6 by default & if this causes problem to emails on a cPanel server, following steps can be used to disable IPv6 on a CentOS 6 cPanel server.

1) In WHM >> Exim Configuration Manager got to advance editor and add following line & save the changes:

disable_ipv6=true

2) To disable IPV6 on modprobe, create a file disable-ipv6.conf on /etc/modprobe.d/ and add the following line which will force the system to execute true instead of loading the IPv6 module:

install ipv6 /bin/true

3) Modify the /etc/sysconfig/network to look as following:

NETWORKING=yes
NETWORKING_IPV6=no
HOSTNAME=server.example.com

4) Stop & disable IPv6 firewall:

service ip6tables stop

chkconfig –del ip6tables

5) Make change to /etc/sysctl.conf by adding following line:

net.ipv6.conf.all.disable_ipv6 = 1

6) Reboot the server for changes to apply.