When deploying Cisco Phones and Call Manager, it may be desirable for the phones to automatically discover the TFTP server/Call Manager in order to download a configuration. This will happen automatically when phones are in the same broadcast domain as the Call Manager Server. However, if your Call Manager server is in a different network, you may need to specify a TFTP server.
This article explains how to specify a TFTP server using DHCP options.
Per Cisco's requirements you may need to enable DHCP Option 150 so that in the DHCP broadcasts, phones can also see a list of all TFTP servers that are connected to the network. The following instructions explain how to configure DHCP options DHCP options for a VLAN on an MX, Z1, or layer-3 MS: