Disable IPv6

• The kernel option ipv6.disable=1 disables the whole IPv6 stack
• If using the kernel option is not possible, add the following parameters to /etc/sysctl.conf:

# Disable IPv6
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.eth0.disable_ipv6 = 1
...

to prevent configuration of IPv6 for listed interfaces.

• To force ntpd to not use IPv6 add -4 to

CMDLINE="/usr/sbin/ntpd -4 -g"

in /etc/rc.d/rc.ntpd

• To force sshd to listen IPv4 only add

# Listen IPv4 only
AddressFamily inet

to the end of /etc/ssh/sshd_config

• To disable IPv6 in sendmail use the option Family=inet in DAEMON_OPTIONS and CLIENT_OPTIONS