Problem with dns - nethserver get same ip on eth0 and br0

(sorry, my englisch is not so good)

my nethserver installation has an unexpected behaivior (in diffrence to similar installations). He has a red and a green interface. the green interface is bridged to the green br0 because of the ndsc on this installation.

The nethserver should be the first dns in my (green) network since few days but he was unreliable. The green ip was ping- and connectable all the time but often there was no answer from the nethserver dns. As reason i found the existence of a ip that exists twice at a time in my network (?). But where the doubled ip comes from? He ist from the nethserver itself!

In the network section from admin panel the eth0 interface has no ip (as it should be) and the br0 bridge has the local ip 192.168.X.2. The ndsc has the ip 192.168.X.3 in the same subnet. The “interface” br0 is shown in my router with his static ip but the eth0 interface is also shown in my router with the same ip (but diffrent mac). So the ip exists twice in one subnet and makes some trouble…

in the router config or with ifconfig i can see that the mac from br0 and eth0 are different. the br0 mac is identical with the mac from vb-nsdc. The mac from eth0 interface is the “real” mac from the network card (a virtual network adapter from prvmox ve).

i have compared my configuration with two other (but similar) nethserver configurations (on different virtual hosts) but i have not found a misconfiguration nor logical knowledge.

In the first other configuration the br0 has the same mac as the connected eth0 interface. In the second other configuration the br0 has the same mac as the nsdc (as in my case).
but in contrast to my nethserver both other configurations works fine!

I have tried to remove, delete, reattached and reconfigured the br0 and eth0 intefaces but the behavior ist always the same. One time i have found the ndsc was connected to eth0 and not to br0 but to correct this makes no difference. I have changed the mac from eth0 interface (change the mac from virtual network adapter) but the problem is the same. the ip appears twice.
Then i have changed the mac from br0 with “ip link set br0 address xyz”. Afterwards the ip wasnt double anymore but the problem thar the dns is anwering unreliable is the same.

Any Ideas? What is the “normal” behavior when bridging a interface? Which mac is normally used to create the bridge or the vb-nsdc? Any suggestion to fix the Problem?

Regards yummiweb