I live in basement and the guy who lives up have 1000mbps telus. He's happy to share internet but doesn't want me to be on his WiFi and I can't add a second router up there as the range doesn't reaches basement and there is no option to wire, so I'm thinking to add my router first after the NOKIA ONT and use LAN port on my router to give his router access.
I'm just wondering will it break anything for him? Like cameras or optiktv or something will stop working? Will his speeds be affected even if I'm not using it? or he can still get 1000mbps on LAN?
If you add your router between the ONT and his, it will break things for him. You want to put a gigabit ethernet switch between the ONT and both routers. Then plug the ONT to one port on the switch and the WAN/Internet ports of each router to two other ports on the switch. Most fibre connections will allow two IP addresses and this way will use two.
While this is true, some have reported issues port forwarding when connected to a bridged Port 1 though it could be down to specific programs that have the issues with that config. There's never been any extensive testing that I know of.