Linux dummy network interfaces can be very handy / 2016-01-29

The recent interruptions in the outside Internet connection made my wish to improve some things in the server at home so internal things keep running through an interruption.

I have to request an IPv6 range for an interface to make wide-dhcpv6-client run, it won't run when I don't configure the interface to assign a /64 to, and my ISP will not route IPv6 when I don't use IPv6 prefix delegation to request the space which is static anyway. But I want the wired and wireless network to have fixed IPv6 ranges so things keep running even when the outside link has a hickup. Solution: request the IPv6 range for a dummy network interface and assign static IPv6 ranges to the ethernet interfaces. In /etc/network/interfaces:

auto dumdh6
iface dumdh6 inet static
    pre-up ip link add name dumdh6 type dummy
    address 0.0.0.0

And in /etc/wide-dhcpv6/dhcp6c.conf:

interface ppp0
{
        send ia-pd 0;

                script "/etc/wide-dhcpv6/dhcp6c-script";
};
id-assoc pd {
        prefix-interface dumdh6 {
                sla-id 3;
        };
};

And there is another dummynet interface to assign the fixed IP addresses to I use for hosting services. This means those services can start (and keep running) even when the link hickups and removes the IP address from the ppp interface. Earlier I did this on an unused vlan interface, but using dummynet feels more tidy.