How does the multi-gig WAN port work on the RAX200?

Hi

I usually use the 'internet' WAN port on my RAX200 to connect the fibre ONT to, and this works without any issues.

However, today i wanted to test the 1g/2.5g WAN port (LAN 1) on the RAX200 so in the router settings, enabled LAN1 as the WAN port and plugged the ONT cat5e LAN cable into LAN1 instead of 'ínternet' port. But with this setup, I'm not getting an internet connection (router rebooted after switching port settings). So is this a bug in the router or have I misunderstood how the multi-gig WAN port (LAN1) works? I've now gone back to using the 'internet' port so its not a big deal but just curious why the multi-gig port didn't work. 

Cheers