Disable IPv6 on CentOS

echo 'install ipv6 /bin/true' > /etc/modprobe.d/ipv6.conf
init 6

This process disables the IPv6 kernel module entirely. It can be considered good form, but by no means necessity, to do the following:

chkconfig ip6tables off

Also in /etc/sysconfig/network-scripts/ifcfg-*:

IPV6INIT=no
IPV6_AUTOCONF=no

To verify, the following should produce empty output:

lsmod | grep v6