Quoting Erick Perez eaperezh@gmail.com:
Aleksandar, can you please explain for me what does a criptic line like "alias net-pf-10 off " means "to disable ipv6" ?
It disables automatic loading of ipv6 module. You can still manually load it by doint "modprobe ipv6" from command line. This was default setting up until 2.4 kernel. In 2.6 kernel default was changed to automatically load ipv6 module as needed.
If you don'thave the above line in /etc/modprobe.conf, each time an application simply attempts to perform IPv6 bind, the kernel would automatically load ipv6 kernel module. The ipv6 module will assigne link local addresses to all interfaces on the system, and it is practically impossible to get rid of the module from that point on (until you reboot machine).
While link local addresses on the interfaces are not really usable to establish communication on the network, many people prefer not to have them assigned. Especially considering the sorry state of IPv6 version of Netfilter. Not only that IPv6 Netfilter lacks many many features of its IPv4 counterpart, the userspace (iptables-ipv6) is not installed by default on CentOS4, redhat-config-security-level will not configure it, and many people run firewalls that are completely open for IPv6 traffic without even realizing it.