DHCP is configured so Cisco IP phones should download their configuration from a TFTP server, but phones fail to load the config. What DHCP configuration is required?

Cisco IP phones require DHCP Option 66 to specify the TFTP server's IP address or hostname from which they should download their configuration files. Without this option, the phones don't know where to find their configuration, leading to a failure in loading it. BOOTP ports 67 (server) and 68 (client) are related to the older BOOTP protocol, which DHCP superseded. While DHCP uses some BOOTP mechanisms, specifying the TFTP server for IP phones is handled by a specific DHCP option, not a port number. DHCP Option 69 is not a standard option used for TFTP server identification for Cisco IP phones; it's typically used for SMTP server information.