NAS542, Link Aggregation and MAC address

Mijzelf

Isn't that my case?

Semi-fixed IP? Yes.

Would there be a conflict?

No. The DHCP server won't hand it over to any other device, as it's reserved for the NAS. The NAS will never ask for it, but just use it. That's fine.

A downside of this approach can be that the nas is not accessible by hostname. Many routers will automatically add the hostnames of the DHCP clients to the DNS system. So in your case that entry might not be there. (Or maybe it does, if fixed IP assignments are also added).

Boyanski

Mijzelf, thank you very much for your valuable support and your time! The script you gave me works and my NAS no longer switches MACs.
I also set a with fixed IP for the NAS and so far it works without noticeable differences. That solves the gateway issue.
The UPnP issues remain, but that is for another topic.