What services are using ipv6 on the server? None! Sounds like a potential security issue. These notes cover disabling ipv6 on Debian Wheezy.
Edit /etc/sysctl.conf and add those parameters to kernel. Also be sure to add extra lines for other network interfaces you want to disable IPv6.
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.eth0.disable_ipv6 = 1
Better yet, create file in /etc/sysctl.d/disable-ipv6.conf with those values
Comment out all the IPV6 hosts in /etc/hosts
Add GRUB_CMDLINE_LINUX_DEFAULT=”ipv6.disable=1 quiet” to /etc/default/grub (grub2)
– for Xen domU add to /boot/grub/menu.lst
You have to reboot the system to make changes take effect.
### IMPORTANT: after editing /etc/default/grub you have to execute “update-grub”
For postfix you have to edit /etc/postfix/main.cf and change (or add) b/c by default it uses both ipv4 and ipv6 and you’ll get warnings on reload of postfix unless you put this
inet_protocols = ipv4
Edit exim4 settings or you’ll get entries in the exim4 paniclog.
Edit /etc/exim4/update-exim4.conf.conf add a new line
and remove the ipv6 stuff from dc_local_interfaces line then execute update-exim4.conf and service exim4 restart.