Why can't I set "Obtain DNS server address automatically"?

When I go in my 64bit Win 7 -->General tab then there are currently two DNS servers entered

Preferred DNS server 8.8.8.8
Alternate DNS server: 192.168.0.1

So in case the first google DNS server fails my router will be contacted and the DNS servers entered there will be used. I told my router in its GUI management to receive the current DNS servers from my cable provider.

Ok, now back in Win TCP-settinsg: I want to tell Win now to ALWAYS use the DNS cable providder settings.

When I try to click the radio button "Obtain DNS server address automatically" then this is NOT possible.
Its greyed out/disabled. Why?

Peter

Do you have a static IP address configured? Obtaining a DNS server automatically requires using a dynamically assigned IP address.

Interesting.

Why is it required to have a dynamic IP address assigned?
What has DNS-Server to do with DHCP server?

Using a static IP address and a DHCP assigned DNS server really doesn't make much sense. In a home network it probably wouldn't make much difference. But Windows 7 isn't just a home computer. In a large network this combination could cause a lot of problems and compromise security. This is not a simple thing.

You can use a statically defined DNS server with a dynamic IP address. But you cannot have a static IP address with a dynamically assigned DNS server.