disable IPv6 (RHEL 5/Centos 5)

Edit /etc/sysconfig/network and change

NETWORKING_IPV6=yes  to  NETWORKING_IPV6=no

Edit /etc/modprobe.d/blacklist and add these lines (if they’re not in it):

blacklist net-pf-10 off
blacklist ipv6 off

Stop the ipv6tables service by typing:

service ip6tables stop

Disable the ipv6tables service by typing:
chkconfig ip6tables off
After these changes, IPv6 will be disabled after the next reboot of your system.

Disabling IPv6 in RHEL 4 / CentOS 4

Just put these in your /etc/modprobe.conf to disable IPv6:

alias net-pf-10 off
alias ipv6 off
install ipv6 /bin/true