Canon LBP7780CX User Manual page 451

[Use ARP/PING]
(3) Click [OK].
IMPORTANT
When the [Use ARP/PING] check box is cleared
You cannot set the IP address using the ARP/PING command.
Proceed to Step
FTP Settings
(1) Click [Edit...] in [FTP Print Settings].
When the check box is selected, you can change the IP address settings from the
client using the ARP/PING command.
6 if you do not specify the settings for the other options.