I set up a sguil sensor at home this weekend, and decided to have it monitor outside my firewall, just because I wanted to know what things looked like out there. This was a version of Linux, and I followed the standard host hardening prescription of turning off unecessary services and interfaces. Since I'm not using IPv6, I wanted to turn support for it off entirely.
Being too lazy to compile my own kernel (good bye, easy updates) I wanted to find a good way to disable IPv6 globally. It turns out that the easiest thing to do is to add the following to your /etc/modules.conf file, then reboot.
alias net-pf-10 off
This prevents the kernel from loading the module that supports IPv6 (called, "ipv6"). This is a CentOS 4.2 box, and I could find no easier way of accomplishing the same thing.