My friend and I are trying to play local co-op games through Parsec. It worked normally when he lived in Hungary, but after moving to Germany and switching to Vodafone internet through a SIM card in his router, Parsec now fails with error 6023. We already tried disabling the Windows Firewall and enabling UPnP on the router. Could this be caused by carrier-grade NAT or the lack of a publicly reachable IPv4 address? Would requesting a public IPv4 address from Vodafone solve it, or is there another workaround?
3 Answers
The most likely cause is the mobile connection using CGNAT, which prevents incoming peer-to-peer connections even if UPnP is enabled. He may need Vodafone to provide a public IPv4 address, or use a VPN that supports incoming port forwarding. Not every VPN can do this, so a regular NordVPN connection may not fix the problem.
Parsec relies heavily on direct peer-to-peer connectivity, so port forwarding can make a big difference. If the router is behind CGNAT, normal port forwarding will not work; a port-forwarding VPN or a public IPv4 address from the provider would be the practical options. You could also test another remote-play tool such as Hamachi-based networking, though that may require configuring the virtual network on both computers.
So an alternative tool might work even if the Vodafone connection stays behind CGNAT, depending on how it establishes the connection?
Avoid leaving the Windows Firewall disabled as a permanent workaround. Turn it back on and create a specific exception for Parsec instead. The firewall is probably not the root issue here; the mobile provider's NAT setup and missing inbound connectivity are much more likely.
That makes sense. He is currently using NordVPN, but it apparently does not offer the kind of port forwarding Parsec needs.