Disabling IPv6 Privacy Extensions in Ubuntu
You may already have noticed (e.g., when your packet filter rules broke after the Ubuntu 12.04 upgrade): Ubuntu 12.04 is forcing IPv6 privacy extensions to be enabled by default. There is a setting in /etc/sysctl.d/10-ipv6-privacy.conf, but it is ignored by Network Manager, which is Ubuntu’s standard facility to establish network connections. At least with Kubuntu there seems to be no configuration option to change this.
Fortunately, one can turn off IPv6 privacy extensions on a per-connection basis by editing the connection details in /etc/NetworkManager/system/connections/:
Just add the setting ip6-privacy=0 to the [ipv6] section of the connection file and you are done.