Configuring both ipv4 and ipv6 with ifupdown

[Frederic Lehobey <Frederic.Lehobey@free.fr>]

Hi,

In sarge, the following /etc/network/interfaces configuration used to
work:

----
auto eth0
iface eth0 inet static
        address 192.168.0.1
        netmask 255.255.255.0

iface eth0 inet6 static
        address 2002:some:addr::1
        netmask 64
----

while in etch if fails with:

# invoke-rc.d networking restart
Reconfiguring network interfaces...SIOCADDRT: File exists
Failed to bring up eth0.
done.

I am ready to file a bug report against ifupdown with severity serious
as it is a regression with respect to working configurations in sarge,
though I ask here before in case I miss something.

I have read bugs #360155, #395826 and #168776 though none of them
seems to be the same as this one.

Thanks for your help,
Frédéric Lehobey