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Windows Server 2025 IPv6 UDP Video Stream Fails, TCP Control Channel Works, Identical Config Works Perfectly on Windows 11 #5198

@dstyleb

Description

@dstyleb

Is there an existing issue for this?

  • I have searched the existing issues

Is your issue described in the documentation?

  • I have read the documentation

Is your issue present in the latest beta/pre-release?

This issue is present in the latest pre-release

Describe the Bug

Environment Information

  • Operating System: Windows Server 2025 with all latest updates
  • Control System: Windows 11 with all latest updates
  • Sunshine Version: latest stable (exact same version on both machines)
  • Network Adapter: Realtek PCIe GbE Family Controller (identical hardware on both machines)
  • Network Environment: Public IPv6, no NAT, Windows Defender Firewall completely disabled
  • Runtime Mode: Desktop process (not service mode), running as full administrator

Problem Description

1. Symptoms:

  • Client successfully connects to Sunshine via TCP port 47990, completes authentication and handshake
  • Immediately after connection establishment, client throws error:  Connection Terminated No video received from host 
  • Wireshark capture shows: only inbound UDP packets (client → server) on ports 47998/48000, no outbound UDP packets (server → client)
  • All packets arrive intact at the server's network interface, but the server kernel never sends any UDP responses

    2. Control Test Results:
  • Exact same network environment, exact same Sunshine configuration, exact same client device
  • Windows 11 machine works 100% correctly with bidirectional UDP traffic
  • Windows Server 2025 machine reproduces the issue 100% of the time

Issues Already Ruled Out

✅ Firewall and port forwarding (Windows Defender Firewall completely disabled)
✅ IPv6 connectivity (TCP works perfectly, ping6 works)
✅ Sunshine configuration (IPv4+IPv6 enabled, listening on [::])
✅ Process permissions (running as full administrator, UserName displays correctly)
✅ IPv6 temporary addresses (both machines have SLAAC Privacy Level=2, Randomize Identifiers=enabled)
✅ Weak host mode (both machines have weakhostsend/weakhostreceive=enabled)
✅ UDP Segmentation Offload (USO) (both machines have IPv6 USO=enabled)
✅ Source address validation (DisableSourceValidation=1 has been set)

Expected Behavior

No response

Additional Context

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Host Operating System

Windows

Operating System Version

Windows server 2025

Architecture

amd64/x86_64

Package

Windows - exe installer

GPU Type

Intel

GPU Model

i3 n305 xe12

GPU Driver/Mesa Version

2025.12

Capture Method

Desktop Duplication API (Windows)

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