What is this needed for? I never set up any port forwarding and don't remember having any issues with network connectivity. But then again I don't play that much online.
I came to ask the same thing - I haven't picked up my Switch in a couple of months but I never touched my router settings for this and it was always working fine. Maybe it's just something from a recent Switch firmware update? Or perhaps just for online play in specific games.
Typically you'd do this for enabling peer-to-peer connections. I run some Minecraft servers in my house this way. I have no idea what kind of peer-to-peer gaming Switch enables. Social gaming is done over the internet with a cloud subscription that costs like $20/year.
I dunno if this had anything to do with it but there is peer to peer online gaming with Divinity Original Sin 2, and I tried grouping up with many folks I friended online and not in the same time zone and it never worked for us. Borderlands also appears to use peer to peer connections.
Yeah this is what I thought, I remember fiddling around with this to make Soulseek (or something) work on my old Linksys WRT54G back when I was at university. I wonder what Switch services/games work this way