I am implementing a VoIP-project with 1200 IP-phones. The desktop PC’s are connected on the PC-port of the IP-phones (built in 3-port switch on the IP-phone). The IP-phones and the PC’s are on the same IP-subnet due to restrictions of the LAN-switches. There are 2 DHCP-servers on the network : a WinNT4.0 serving the PC’s and a unix-based IP-PBX serving the IP-phones. The IP-PBX responds only for request of the IP-phones with the help of the option 60 = Vendorclass info And the IP-phones give priority to offers coming from this IP-PBX with the help of the option 43 = Vendor specific info. Now when the IP-PBX is down for maintenance purposes the IP-phones get served from the WinNT DHCP-server because there is nothing to give priority for. This is not wanted. Therefore I wanted to exclude all the IP-phones based on the range of MAC-address to get there IP-addresses from the WinNT DHCP-server. But this is not possible on WinNT4.0 DHCP-server. Now I am looking for DHCP-server applications that can do this. Can anybody help me on this subject? Thanks.