Re: IPv6 and IP in parallel

Hi Thomas,

On 08/26/14 11:35, Thomas Haller wrote:
On Tue, 2014-08-26 at 08:30 +0200, Harald Dunkel wrote:

So it sees the IPv6 configuration on eth0 coming from somewhere,
doesn't find a connection configuration for it, takes eth0 as it
is and doesn't setup IPv4?

I think they come from:

        auto eth0
        iface eth0 inet dhcp
        iface eth0 inet6 auto

This is a misunderstanding. These config lines are usually
commented out. I manually enable these lines if n-m is not
used, just for verification.

AFAICS IPv6 is autoconfigured very early at boot time, either
by the kernel itself, by some code on the initrd, or by one of
the few tools run in rescue mode (systemd, udev, bluetoothd,
dbus-daemon). There is no such "autoconf" functionality for

I am using Debian, but according to an Ubuntu bug report this
happens even before the sysctl.conf file is read, i.e. you
cannot override this autoconfiguration. See

Of course I tried. I have set

        net.ipv6.conf.all.autoconf = 0
        net.ipv6.conf.all.accept_ra = 0

in systctl.conf and rebooted with systemd.unit=rescue.
Network-manager was not started. /etc/network/interfaces doesn't
mention eth0, either. And yet I've got a global IPv6 address for

maybe dhcp4 is not yet complete when NM starts and NM thinks that IPv4
is disabled.

A solution might be to remove "auto eth0" if you want to use NM.

Do you think this could be improved?

generating a connection involves lots of guess work, and cannot always
work correctly. It should be improved as particular failure cases are

IMHU IPv4 and IPv6 are separate
protocols with different means for configuration and very little in
common. Shouldn't n-m use/create separate connections for these

A "connection" (in NM terms) is a configuration profile that you can
activate. Since NM generates *one* connection to match what it sees, the
connection has configuration for both IPv4 and IPv6.

I understand that n-m tries the best it can to "guess" a connection
profile according to the current configuration of eth0. Since IPv4
is not configured yet (contrary to IPv6), it never will be.

What would you suggest to get out of this dilemma?


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