I had the same Issue, you may configured ETH1 instead of ETH0 on Polycom KIRK 600v3 Webinterface. In My case i turned off DHCP and deleted all IP adress entries on ETH0. I mentioned it, after i rebooted the UC540; the Polycom KIRK 600v3 tried to register ephones under IP:192.168.0.1, which was configured on ETH0.
Maybe it use ETH0 before it switches to ETH1.