Configuring native IPv6 in Debian, dual stacked with IPv4

The easiest way to configure a host for IPv6 use is to use router
advertisements, if your network provides them. That works out of the box with
zero configuration, even without any IPv6 thing in /etc/network/interfaces.
However, for servers you're usually better off using static addresses.

There are a few options to configure a static address in Debian. Using the
"inet6" option in /etc/network/interfaces caused me a minor headache: there
does not appear to be any nice way to configure multiple addresses, and the
"netmask" thing just feels awkward when everything else uses slashes to
indicate prefix length.

Eventually I settled on using good old "inet" with the "up" option, which is an
alias for "post-up" and declares arbitrary shell commands to be executed after
the ipv4 configuration stuff is done. So, in /etc/network/interfaces:

The "ip" utility can be found in the package "iproute".

    auto eth0
    iface eth0 inet static
        address 192.168.1.2
        netmask 255.255.255.0
        gateway 192.168.1.1
        up modprobe ipv6 || true
        up ip -6 addr add 2001:db8:a:f::2/64 dev $IFACE
        up ip -6 route add default via 2001:db8:a:f::1

Any number of additional static IP addresses and routes can be added:

        up ip -6 addr add 2001:db8:a:d::1/64 dev $IFACE
        up ip -6 route add 2001:db8:b::/48 via 2001:db8:a:d::2


References:
* http://www.melb.apana.org.au/wiki/IPv6ConfigurationForDebian