Debian linux running a 2.6 kernel
To disable IPv6 you need both the following lines in your /etc/modprobe.conf file
alias ipv6 off alias net-pf-10 off
Thanks to the guys on the #debian freenode channel for help with this.
Moved the config to /etc/modprobe.d/local
This stopped working on 2.6.18 on debian etch. Now my /etc/modprobe.d/local now contains just
Apparently - in some cases this may still not work - in that case it is possible to try
install ipv6 /bin/true