Dark fiber

[3x-t]

Hi,

We have dark fiber lines in our two BO going back to the HQ. I'm not sure how to configure HQ and BO FortiGate's (200F and 100F) to use it.
I have DWDM SFP on both sides, same channel...
How should I configure the interface? As WAN or LAN?
There should be some encryption between sites. Should I create a site-to-site VPN?
Should I create SD-WAN as an "Inside" zone and add an interface that is in use by dark fiber?

Any help is much appreciated!

Thanks

[AlexC-FTNT]

This just popped up, probably too late and you already found a solution.

'dark fiber' ~ a cable >> Probably connecting 2 locations. What you do with it is entirely up to you. Assigning IP addresses on both ends would be a start. Sure, you can add encryption (site-to-site VPN). LAN or WAN ? if you connect your BO to internet through this connection, then WAN. Otherwise LAN/DMZ. It's a label after all. Same about SDWAN. You could do that.