CentOS / RHEL 7 : How to disable IPv6

By | February 21, 2017

Post describes procedure to disable IPv6 on CentOS/RHEL 7. There are 2 ways to do this :
1. Disable IPv6 in kernel module (requires reboot)
2. Disable IPv6 using sysctl settings (no reboot required)

To verify if IPv6 is enabled or not, execute :

# ifconfig -a | grep inet6
        inet6 fe80::211:aff:fe6a:9de4  prefixlen 64  scopeid 0x20
        inet6 ::1  prefixlen 128  scopeid 0x10

1. Disable IPv6 in kernel module (requires reboot)

1. Edit /etc/default/grub and add ipv6.disable=1 in line GRUB_CMDLINE_LINUX, e.g.:

# cat /etc/default/grub
GRUB_CMDLINE_LINUX="ipv6.disable=1 crashkernel=auto rhgb quiet"

2. Regenerate a GRUB configuration file and overwrite existing one:

# grub2-mkconfig -o /boot/grub2/grub.cfg

3. Restart system and verify no line “inet6” in “ip addr show” command output.

# shutdown -r now
# ip addr show | grep net6

2. Disable IPv6 using sysctl settings (no reboot required)

1. Append below lines in /etc/sysctl.conf:

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
NOTE : To disable IPv6 on a single interface add below lines to /etc/sysctl.conf :
net.ipv6.conf.[interface].disable_ipv6 = 1 ### put interface name here [interface]
net.ipv6.conf.default.disable_ipv6 = 1

2. To make the settings affective, execute :

# sysctl -p
NOTE : make sure the file /etc/ssh/sshd_config contains the line AddressFamily inet to avoid breaking SSH Xforwarding if you are using the sysctl method

3. Add the AddressFamily line to sshd_config :

# vi /etc/ssh/sshd_config
AddressFamily inet

Restart sshd for changes to get get effect :

# systemctl restart sshd
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