dhcpcd-discuss

I try to setup a bridge with usb and eth0
My goal:
if no cable is plugged in:
Bridge link is down. I need an ipv4all address.
if a cable is plugged in in eth0:
 Bridge link is up. So I try to get IP immediate from dhpc server or an ipv4all address.

To get the an IP immediately, I use "release" in dhcpcd.conf.
But how to realize the first thing when bridge is down? "nolink" in dhcpcd.conf is not an option because to get an IP immediately is not working than.

Any ideas how to solve my goals?

Thank you for your suggestions & time

Matthias