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

AddressFamily inet

to /etc/ssh/sshd_config

• To force httpd to listen IPv4 only, specify an IPv4 address on all Listen directives, for example,

Listen 0.0.0.0:80

(in /etc/httpd/httpd.conf and/or /etc/httpd/extra/httpd-ssl.conf)

• To disable IPv6 in bind put

NAMED_OPTIONS="-4"

to /etc/default/named and add

filter-aaaa-on-v4 yes;

to options in /etc/named.conf

• To disable IPv6 in postfix use the option inet_protocols in /etc/postfix/main.cf
• To disable IPv6 in sendmail use the option Family=inet in DAEMON_OPTIONS and CLIENT_OPTIONS