Here's how to disable the protocol on a Red Hat-based system:

1. Open a terminal window.
2. Change to the root user.
3. Issue the command sysctl -w net.ipv6.conf.all.disable_ipv6=1
4. Issue the command sysctl -w net.ipv6.conf.default.disable_ipv6=1

To re-enable IPv6, issue the following commands:

sysctl -w net.ipv6.conf.all.disable_ipv6=0
sysctl -w net.ipv6.conf.default.disable_ipv6=0

Here's how to disable the protocol on a Debian-based machine.

1. Open a terminal window.
2. Issue the command sudo nano /etc/sysctl.conf
3. Add the following at the bottom of the file:
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
4. Save and close the file.
5. Reboot the machine.

To re-enable IPv6, remove the above lines from /etc/sysctl.conf and reboot the machine.