Comment # 19 on bug 1135647 from Marius Tomaschewski

(In reply to andreas bittner from comment #17)
> in the systems current (buggy?) state:
> 
> systemctl show -p Id network.service
> Id=wicked.service
     ^^^^^^^^^^^^^^

Yes.

wicked.service is currently selected as the network.service, but somehow also
NetworkManager has been enabled + started as visible in comment 15:

>    Loaded: loaded (/usr/lib/systemd/system/NetworkManager.service; enabled; vendor preset: disabled)

It is possible that some Desktop applet configured this. Wicked does not
provide a desktop applet / desktop integration yet. A desktop applet may
request root privileges and enable NetworkManager with some click...

When both are running, they're trying to make the same thing (dhcp6) but
differently and conflict with each other. Both can request dhcp6 [it is
using multicasts from fe80:* to ff:* addresses], but only one will get
*all* answers, the another no response.

Beside this, while wicked is using the auto-configuration provided by
the kernel, NetworkManager is *AFAIK* disabling it and using a library
instead.

Further, the machine is currently configured as *router* with:

net.ipv4.conf.all.forwarding = 1

net.ipv6.conf.all.forwarding = 1

Did you tried to configure e.g. VPN?

IPv6 auto-configuration of Routers is _disabled_ by default acc. to RFCs.
To enable it on a router e.g. to get the ipv6 default route applied again,
you need to explicitly enable it using:

net.ipv6.conf.eth0.accept_ra = 2

instead of 1 (1 is for hosts which have forwarding = 0), see also:

https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt

(In reply to andreas bittner from comment #18)
> Also: what is default for leap these days? What do I go for? wicked?
> networkmanager? I never needed to really think about this kind of stuff.

It depends on the installation pattern. Desktop/Laptop pattern can request
to use NetworkManager and yast2 may switch over then.

A while ago, there were some bug in an application that were adding an RPM
dependency to NetworkManager -- seems it were this bug:
 http://bugzilla.opensuse.org/show_bug.cgi?id=1122194

I've observed on ARM (Raspberry PI), that some images are broken and enable
to start both or improperly enable/disable one of them ... except this was
some dependency like above again...?