Disabling IPV6

There is a few ways to disable IPV6.  There are two methods for system-wide, and one method to disable per interface..  This is for general networking, rather than comparing to problems with IPV6 within Mozilla Firefox, which requires a completely alternative method.  Although this could apply if you've already tried the Firefox issue, and it's still not working.  Some network cards, such as the Realtek 8139's, can have issues with IPV6 that affect all network traffic.

Some systems will work with one or the other, or even both of the system-wide solutions.

1. Disabling in /etc/modprobe.conf:

Edit /etc/modprobe.conf and add the following lines:

alias net-pf-10 off
alias ipv6 off

2. Disabling in /etc/sysconfig/network: 

Edit /etc/sysconfig/network and add the following line:

NETWORKING_IPV6=no

To disable at interface level, you would use this method.  That way, you can leave IPV6 enabled for some interfaces, and not others (if you have multiple network cards):

Edit /etc/sysconfig/network-scripts/ifcfg-xxxx (where xxxx is eth0, wlan0 or whatever your interface is) and add the following:

IPV6INIT=no

And that should take care of disabling IPV6 for you.