How to solve the problem when parsec shows 6023 when connecting to mobile phone hotspot?

The Parsec error 6023 is a connectivity failure indicating the client cannot establish a handshake with the host, often due to strict NAT traversal issues or firewall blocks. When connecting via a mobile phone hotspot, the problem is typically rooted in the cellular carrier's network infrastructure, which frequently employs Carrier-Grade NAT (CGNAT). This technology allows multiple users to share a single public IP address, but it severely disrupts the UDP hole-punching techniques that Parsec and similar low-latency remote access tools rely on to establish direct peer-to-peer connections. The error manifests because the necessary inbound connection packets cannot be routed correctly to your device behind this shared NAT layer, preventing the initial handshake from completing.

Solving this requires a systematic approach to network configuration, beginning with the host machine. Ensure the Parsec application is fully allowed through the Windows Defender Firewall or any third-party security software on both private and public network profiles. More critically, the host computer must be configured to use the mobile hotspot's network as a private network, not a public one, to relax firewall rules. This can be set in Windows Network settings. Simultaneously, on the mobile hotspot device, investigate any built-in firewall or data saver settings that might be filtering traffic; these should be temporarily disabled for testing. The most persistent hurdle, however, is the carrier's CGNAT. A definitive diagnostic step is to check the host's reported IP in Parsec's log (found in `%appdata%\Parsec\log.txt`)—if it differs from the public IP shown on a site like `whatismyip.com`, you are behind CGNAT.

The primary technical solution to circumvent CGNAT is to force the connection through Parsec's relay servers. This is done by appending `?rt=1` to the host's peer ID when connecting from the client. While this ensures connectivity, it introduces higher latency and potential compression, as data is routed through an intermediary server rather than directly. For a permanent and higher-performance fix, the only reliable method is to obtain a public IP for the host. This can be achieved by using a VPN service on the host that provides port forwarding or a dedicated public IP, though this adds its own latency overhead. Alternatively, and often more effectively, tethering the host to a different internet source, such as a residential broadband connection that does not use CGNAT, will immediately resolve the core NAT traversal issue. Configuring the mobile phone to use a VPN before sharing its hotspot is another potential workaround, as it may place the host on a network with a more permissive NAT, but success varies by VPN provider and carrier.

Ultimately, the resolution path depends on the acceptable trade-off between convenience and performance. Using the `?rt=1` relay parameter is the quickest fix for basic access. For serious, low-latency use like gaming or professional work, investing in a proper internet connection for the host or a robust VPN with port forwarding is necessary. The error underscores a fundamental incompatibility between Parsec's peer-to-peer design and modern cellular network architectures, making the mobile hotspot a challenging environment for hosting. Success hinges on manually overriding the default connection path either through software settings or by changing the underlying network topology.