Oh my, thank you. I was faffing about with 1-to-1 and Port Forwarding.
To a potential future reader:
"fibre" is my alias for the IP of the ONT, 192.168.24.2, "WAN_FIBRE" is the Interface I designated for this network.
To a potential future reader:
Code Select
Interface Source Source Port Destination Destination Port NAT Address NAT Port
WAN_FIBRE any * fibre * WAN_FIBRE address *
"fibre" is my alias for the IP of the ONT, 192.168.24.2, "WAN_FIBRE" is the Interface I designated for this network.