With the upcoming season of Classic, I would like everyone to use Direct Connect for netplay. As of this date (10/14/2019), relay server is not working.
This is actually very simple to set up. Just requires a few minutes of work, and more time to find the instructions for your router/modem.
Check out this video from therexershow - RetroArch - How to Set up Port Forwarding
When playing a game against someone via netplay (P2P - Peer to Peer), one player acts