IPv6 configuration on Ubuntu (dapper) systems

How can I enable/disable IPv6 globally?

Ubuntu dapper default supports IPv6, so you have to do nothing to enable IPv6. If you want do disable IPv6 globally, please read [:IPv6hostslinux disableIPv6:our section] on how to do it.

How can I enable forwarding between IPv6 enabled interfaces?

In /etc/sysctl.conf add the line

net/ipv6/conf/all/forwarding=1

and run

# sysctl -p /etc/sysctl.conf

Please note, you cannot enable/disable IPv6 forwarding per interface as in the IPv4 case. If you want to disable IPv6 forwarding for some interfaces, use netfilter/p6tables.

How can I enable/disable autoconfiguration on all interfaces?

Autoconfiguration is enabled by default. If you want to disable it for all interfaces, add the line

net/ipv6/conf/all/autoconf=0

to /etc/sysctl.conf and reload the file by sysctl as it is shown above.

How can I enable/disable router behaviour (i.e not to accept router advertisements) on all devices?

The kernel default accepts router advertisements. You can disable it on all interfaces by adding the line

net/ipv6/conf/all/accept_ra=0

to /etc/sysctl.conf and reloading it by sysctl.

How can I configure an interface statically with global IPv6 address?

Use the standard /etc/network/interfaces file on Debian/Ubuntu systems:

    iface eth0 inet6 static
        address dead:beef::1
        netmask 64

If you set your system to ignore router advertisements then you have to add a static default gateway as well:

    iface eth0 inet6 static
        address dead:beef::1
        netmask 64
        gateway dead:beef::

Please note, you cannot bring up just the IPv6 settings of an interface, so in order your changes take effect you have to issue the commands

# ifdown eth0
# ifup eth0

which first brings down IPv4 on your interface.

How can I set up a default gateway via an interface instead of an IPv6 address?

You can use the post-up and pre-down options to call ip and set the default gateway in /etc/network/interfaces:

    iface eth0 inet6 static
        address dead:beef::1
        netmask 64
        post-up ip -6 route add ::/0 dev eth0
        pre-down ip -6 route del ::/0 dev eth0

How can I setup an IPv6 over IPv4 tunnel?

This is also quite simple. In /etc/network/interfaces write

    iface eth0 inet6 v4tunnel
        address dead:beef::1
        netmask 64
        endpoint 192.168.0.1    # Address of other tunnel endpoint