How do I disable IPv6 on CentOS 6? 

Ifconfig shows an inet6-line:
 
# ifconfig
 
# vi /etc/modprobe.conf
Add lines below:

# create new
alias ipv6 off
alias net-pf-10 off
Save and exit vi.
 
# reboot
 
# ifconfig
Ifconfig doesn't show an inet6-line any more.