Sunshine getting MTU wrong on virtual windows 11 machine that has been setup using a Virtio (paravirtualized) nic

[stevedh42]

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

When Running Sunshine on a proxmox virtual machine that has been setup using a Virtio (paravirtualized) nic it tries to send the video using udp packets that are larger then 10k. The adapter MTU in the adapter is set to 1500. This results in all moonlight clients getting a 'Connection Terminated No video received from host' error.

On checking in wireshark, sunshine tries to send packets > 10k, when they arrive at moonlight they have been truncated to 1500.

I want to use this virtual adapter as it allows a greater then 1g connection. The physical nat is 2.5G, although the virtual adapter reports it as 10G.

Note that when I replace the virtio network adapter with a virtual intel 1g adapter it correctly gets the mtu size and moonlight can get the video steam fine.

C:\Users\steve>netsh interface ipv4 show interfaces

Idx Met MTU State Name

---

1 75 1450 connected Loopback Pseudo-Interface 1
11 15 1450 connected Ethernet

C:\Users\steve>netsh interface ipv4 show subinterfaces

   MTU  MediaSenseState      Bytes In     Bytes Out  Interface

---

  1450                1             0         29395  Loopback Pseudo-Interface 1
  1450                1      22869248       7735395  Ethernet

PS C:\Users\steve> $adapter = get-netadapter Ethernet
PS C:\Users\steve> $adapter.MtuSize
1500
PS C:\Users\steve> $adapter.DriverDescription
Red Hat VirtIO Ethernet Adapt

Expected Behavior

Sunshine should send packets that fit within the MTU size, or provide an option that allows this to be set manually.

Additional Context

No response

Host Operating System

Windows

Operating System Version

Edition Windows 11 Pro Version 25H2 Installed on ‎07/‎03/‎2026 OS build 26200.8037 Experience Windows Feature Experience Pack 1000.26100.300.0

Architecture

amd64/x86_64

Package

Windows - portable (NOT recommended)

GPU Type

NVIDIA

GPU Model

NVidia GTX 506

GPU Driver/Mesa Version

Driver Version: 595.79 CUDA Version: 13.2

Capture Method

None

Apps

Log output

[2026-03-23 10:44:19.958]: Info: Sunshine version: 2026.323.32542 commit: 3e06afab1f45171d675ecaa45d8bcdd58c85eca5
[2026-03-23 10:44:19.958]: Info: Package Publisher: LizardByte
[2026-03-23 10:44:19.959]: Info: Publisher Website: https://app.lizardbyte.dev
[2026-03-23 10:44:19.959]: Info: Get support: https://app.lizardbyte.dev/support
[2026-03-23 10:44:19.959]: Info: Provided workaround settings for SettingsManager:
{
  "hdr_blank_delay": null
}
[2026-03-23 10:44:19.963]: Info: Currently available display devices:
[
  {
    "device_id": "{c6354dd2-42f1-5690-9108-f64d477f3041}",
    "display_name": "\\\\.\\DISPLAY1",
    "edid": {
      "manufacturer_id": "NAX",
      "product_code": "0CCD",
      "serial_number": 0
    },
    "friendly_name": "4K60/1080P120",
    "info": {
      "hdr_state": null,
      "origin_point": {
        "x": 0,
        "y": 0
      },
      "primary": true,
      "refresh_rate": {
        "type": "rational",
        "value": {
          "denominator": 1000,
          "numerator": 59934
        }
      },
      "resolution": {
        "height": 1080,
        "width": 1920
      },
      "resolution_scale": {
        "type": "rational",
        "value": {
          "denominator": 100,
          "numerator": 100
        }
      }
    }
  }
]
[2026-03-23 10:44:20.115]: Info: nvprefs: No need to modify application profile settings
[2026-03-23 10:44:20.115]: Info: nvprefs: Changed OGL_CPL_PREFER_DXPRESENT to OGL_CPL_PREFER_DXPRESENT_PREFER_ENABLED for base profile
[2026-03-23 10:44:20.171]: Info: Compiling shaders...
[2026-03-23 10:44:20.237]: Info: Compiled shaders
[2026-03-23 10:44:20.246]: Error: Couldn't get default audio endpoint [0x80070490]
[2026-03-23 10:44:20.259]: Info: // Testing for available encoders, this may generate errors. You can safely ignore those errors. //
[2026-03-23 10:44:20.262]: Info: Trying encoder [nvenc]
[2026-03-23 10:44:20.545]: Info: 
Device Description : NVIDIA GeForce RTX 5060
Device Vendor ID   : 0x000010DE
Device Device ID   : 0x00002D05
Device Video Mem   : 7895 MiB
Device Sys Mem     : 0 MiB
Share Sys Mem      : 16374 MiB
Feature Level      : 0x0000B100
Capture size       : 1920x1080
Offset             : 0x0
Virtual Desktop    : 1920x1080
[2026-03-23 10:44:20.545]: Info: Active GPU has HAGS enabled
[2026-03-23 10:44:20.545]: Info: Using realtime GPU priority
[2026-03-23 10:44:20.546]: Info: 
Colorspace         : DXGI_COLOR_SPACE_RGB_FULL_G22_NONE_P709
Bits Per Color     : 8
Red Primary        : [0.679688,0.30957]
Green Primary      : [0.206055,0.693359]
Blue Primary       : [0.151367,0.0546875]
White Point        : [0.313477,0.329102]
Min Luminance      : 0.5 nits
Max Luminance      : 270 nits
Max Full Luminance : 270 nits
[2026-03-23 10:44:20.547]: Info: Desktop resolution [1920x1080]
[2026-03-23 10:44:20.548]: Info: Desktop format [DXGI_FORMAT_B8G8R8A8_UNORM]
[2026-03-23 10:44:20.548]: Info: Display refresh rate [59.934Hz]
[2026-03-23 10:44:20.548]: Info: Requested frame rate [60/1 exactly 60 fps]
[2026-03-23 10:44:20.548]: Info: Creating encoder [h264_nvenc]
[2026-03-23 10:44:20.548]: Info: Color coding: SDR (Rec. 601)
[2026-03-23 10:44:20.548]: Info: Color depth: 8-bit
[2026-03-23 10:44:20.548]: Info: Color range: JPEG
[2026-03-23 10:44:20.597]: Info: NvEnc: created encoder H.264 P1 async two-pass rfi
[2026-03-23 10:44:20.625]: Info: Creating encoder [hevc_nvenc]
[2026-03-23 10:44:20.625]: Info: Color coding: SDR (Rec. 601)
[2026-03-23 10:44:20.626]: Info: Color depth: 8-bit
[2026-03-23 10:44:20.626]: Info: Color range: JPEG
[2026-03-23 10:44:20.670]: Info: NvEnc: created encoder HEVC P1 async two-pass rfi
[2026-03-23 10:44:20.696]: Info: Creating encoder [av1_nvenc]
[2026-03-23 10:44:20.696]: Info: Color coding: SDR (Rec. 601)
[2026-03-23 10:44:20.696]: Info: Color depth: 8-bit
[2026-03-23 10:44:20.697]: Info: Color range: JPEG
[2026-03-23 10:44:20.743]: Info: NvEnc: created encoder AV1 P1 async two-pass rfi
[2026-03-23 10:44:20.771]: Info: Creating encoder [h264_nvenc]
[2026-03-23 10:44:20.771]: Info: Color coding: SDR (Rec. 601)
[2026-03-23 10:44:20.771]: Info: Color depth: 8-bit
[2026-03-23 10:44:20.772]: Info: Color range: JPEG
[2026-03-23 10:44:20.821]: Info: NvEnc: created encoder H.264 P1 async yuv444 two-pass rfi
[2026-03-23 10:44:21.079]: Info: 
Device Description : NVIDIA GeForce RTX 5060
Device Vendor ID   : 0x000010DE
Device Device ID   : 0x00002D05
Device Video Mem   : 7895 MiB
Device Sys Mem     : 0 MiB
Share Sys Mem      : 16374 MiB
Feature Level      : 0x0000B100
Capture size       : 1920x1080
Offset             : 0x0
Virtual Desktop    : 1920x1080
[2026-03-23 10:44:21.080]: Info: Active GPU has HAGS enabled
[2026-03-23 10:44:21.080]: Info: Using realtime GPU priority
[2026-03-23 10:44:21.080]: Info: 
Colorspace         : DXGI_COLOR_SPACE_RGB_FULL_G22_NONE_P709
Bits Per Color     : 8
Red Primary        : [0.679688,0.30957]
Green Primary      : [0.206055,0.693359]
Blue Primary       : [0.151367,0.0546875]
White Point        : [0.313477,0.329102]
Min Luminance      : 0.5 nits
Max Luminance      : 270 nits
Max Full Luminance : 270 nits
[2026-03-23 10:44:21.081]: Info: Desktop resolution [1920x1080]
[2026-03-23 10:44:21.082]: Info: Desktop format [DXGI_FORMAT_B8G8R8A8_UNORM]
[2026-03-23 10:44:21.082]: Info: Display refresh rate [59.934Hz]
[2026-03-23 10:44:21.082]: Info: Requested frame rate [60/1 exactly 60 fps]
[2026-03-23 10:44:21.082]: Info: Creating encoder [hevc_nvenc]
[2026-03-23 10:44:21.082]: Info: Color coding: SDR (Rec. 709)
[2026-03-23 10:44:21.082]: Info: Color depth: 10-bit
[2026-03-23 10:44:21.082]: Info: Color range: JPEG
[2026-03-23 10:44:21.199]: Info: NvEnc: created encoder HEVC P1 async yuv444 10-bit two-pass rfi
[2026-03-23 10:44:21.248]: Info: Creating encoder [av1_nvenc]
[2026-03-23 10:44:21.248]: Info: Color coding: SDR (Rec. 709)
[2026-03-23 10:44:21.248]: Info: Color depth: 10-bit
[2026-03-23 10:44:21.248]: Info: Color range: JPEG
[2026-03-23 10:44:21.321]: Error: NvEnc: gpu doesn't support YUV444 encode
[2026-03-23 10:44:21.321]: Error: NvEnc: NvEncUnregisterAsyncEvent() failed: NV_ENC_ERR_DEVICE_NOT_EXIST
[2026-03-23 10:44:21.348]: Info: Creating encoder [av1_nvenc]
[2026-03-23 10:44:21.348]: Info: Color coding: SDR (Rec. 709)
[2026-03-23 10:44:21.348]: Info: Color depth: 10-bit
[2026-03-23 10:44:21.348]: Info: Color range: JPEG
[2026-03-23 10:44:21.393]: Info: NvEnc: created encoder AV1 P1 async 10-bit two-pass rfi
[2026-03-23 10:44:21.433]: Info: 
[2026-03-23 10:44:21.433]: Info: // Ignore any errors mentioned above, they are not relevant. //
[2026-03-23 10:44:21.433]: Info: 
[2026-03-23 10:44:21.433]: Info: Found H.264 encoder: h264_nvenc [nvenc]
[2026-03-23 10:44:21.433]: Info: Found HEVC encoder: hevc_nvenc [nvenc]
[2026-03-23 10:44:21.433]: Info: Found AV1 encoder: av1_nvenc [nvenc]
[2026-03-23 10:44:21.433]: Info: Starting system tray
[2026-03-23 10:44:21.433]: Info: System tray thread initialized successfully
[2026-03-23 10:44:21.434]: Info: No main thread features enabled, skipping event loop
[2026-03-23 10:44:21.434]: Info: System tray thread started
[2026-03-23 10:44:21.436]: Info: Configuration UI available at [https://localhost:47990]
[2026-03-23 10:44:21.452]: Info: System tray created
[2026-03-23 10:44:22.194]: Info: Registered Sunshine mDNS service
[2026-03-23 10:45:52.959]: Info: Encoder reenumeration is required
[2026-03-23 10:45:52.959]: Info: // Testing for available encoders, this may generate errors. You can safely ignore those errors. //
[2026-03-23 10:45:52.959]: Info: Trying encoder [nvenc]
[2026-03-23 10:45:53.242]: Info: 
Device Description : NVIDIA GeForce RTX 5060
Device Vendor ID   : 0x000010DE
Device Device ID   : 0x00002D05
Device Video Mem   : 7895 MiB
Device Sys Mem     : 0 MiB
Share Sys Mem      : 16374 MiB
Feature Level      : 0x0000B100
Capture size       : 1920x1080
Offset             : 0x0
Virtual Desktop    : 1920x1080
[2026-03-23 10:45:53.242]: Info: Active GPU has HAGS enabled
[2026-03-23 10:45:53.242]: Info: Using realtime GPU priority
[2026-03-23 10:45:53.243]: Info: 
Colorspace         : DXGI_COLOR_SPACE_RGB_FULL_G22_NONE_P709
Bits Per Color     : 8
Red Primary        : [0.679688,0.30957]
Green Primary      : [0.206055,0.693359]
Blue Primary       : [0.151367,0.0546875]
White Point        : [0.313477,0.329102]
Min Luminance      : 0.5 nits
Max Luminance      : 270 nits
Max Full Luminance : 270 nits
[2026-03-23 10:45:53.244]: Info: Desktop resolution [1920x1080]
[2026-03-23 10:45:53.245]: Info: Desktop format [DXGI_FORMAT_B8G8R8A8_UNORM]
[2026-03-23 10:45:53.245]: Info: Display refresh rate [59.934Hz]
[2026-03-23 10:45:53.245]: Info: Requested frame rate [60/1 exactly 60 fps]
[2026-03-23 10:45:53.245]: Info: Creating encoder [h264_nvenc]
[2026-03-23 10:45:53.245]: Info: Color coding: SDR (Rec. 601)
[2026-03-23 10:45:53.245]: Info: Color depth: 8-bit
[2026-03-23 10:45:53.245]: Info: Color range: JPEG
[2026-03-23 10:45:53.291]: Info: NvEnc: created encoder H.264 P1 async two-pass rfi
[2026-03-23 10:45:53.392]: Info: Creating encoder [hevc_nvenc]
[2026-03-23 10:45:53.392]: Info: Color coding: SDR (Rec. 601)
[2026-03-23 10:45:53.392]: Info: Color depth: 8-bit
[2026-03-23 10:45:53.392]: Info: Color range: JPEG
[2026-03-23 10:45:53.438]: Info: NvEnc: created encoder HEVC P1 async two-pass rfi
[2026-03-23 10:45:53.463]: Info: Creating encoder [av1_nvenc]
[2026-03-23 10:45:53.463]: Info: Color coding: SDR (Rec. 601)
[2026-03-23 10:45:53.463]: Info: Color depth: 8-bit
[2026-03-23 10:45:53.463]: Info: Color range: JPEG
[2026-03-23 10:45:53.510]: Info: NvEnc: created encoder AV1 P1 async two-pass rfi
[2026-03-23 10:45:53.536]: Info: Creating encoder [h264_nvenc]
[2026-03-23 10:45:53.536]: Info: Color coding: SDR (Rec. 601)
[2026-03-23 10:45:53.536]: Info: Color depth: 8-bit
[2026-03-23 10:45:53.536]: Info: Color range: JPEG
[2026-03-23 10:45:53.583]: Info: NvEnc: created encoder H.264 P1 async yuv444 two-pass rfi
[2026-03-23 10:45:53.848]: Info: 
Device Description : NVIDIA GeForce RTX 5060
Device Vendor ID   : 0x000010DE
Device Device ID   : 0x00002D05
Device Video Mem   : 7895 MiB
Device Sys Mem     : 0 MiB
Share Sys Mem      : 16374 MiB
Feature Level      : 0x0000B100
Capture size       : 1920x1080
Offset             : 0x0
Virtual Desktop    : 1920x1080
[2026-03-23 10:45:53.848]: Info: Active GPU has HAGS enabled
[2026-03-23 10:45:53.848]: Info: Using realtime GPU priority
[2026-03-23 10:45:53.848]: Info: 
Colorspace         : DXGI_COLOR_SPACE_RGB_FULL_G22_NONE_P709
Bits Per Color     : 8
Red Primary        : [0.679688,0.30957]
Green Primary      : [0.206055,0.693359]
Blue Primary       : [0.151367,0.0546875]
White Point        : [0.313477,0.329102]
Min Luminance      : 0.5 nits
Max Luminance      : 270 nits
Max Full Luminance : 270 nits
[2026-03-23 10:45:53.850]: Info: Desktop resolution [1920x1080]
[2026-03-23 10:45:53.850]: Info: Desktop format [DXGI_FORMAT_B8G8R8A8_UNORM]
[2026-03-23 10:45:53.850]: Info: Display refresh rate [59.934Hz]
[2026-03-23 10:45:53.850]: Info: Requested frame rate [60/1 exactly 60 fps]
[2026-03-23 10:45:53.850]: Info: Creating encoder [hevc_nvenc]
[2026-03-23 10:45:53.851]: Info: Color coding: SDR (Rec. 709)
[2026-03-23 10:45:53.851]: Info: Color depth: 10-bit
[2026-03-23 10:45:53.851]: Info: Color range: JPEG
[2026-03-23 10:45:53.964]: Info: NvEnc: created encoder HEVC P1 async yuv444 10-bit two-pass rfi
[2026-03-23 10:45:54.025]: Info: Creating encoder [av1_nvenc]
[2026-03-23 10:45:54.025]: Info: Color coding: SDR (Rec. 709)
[2026-03-23 10:45:54.025]: Info: Color depth: 10-bit
[2026-03-23 10:45:54.025]: Info: Color range: JPEG
[2026-03-23 10:45:54.106]: Error: NvEnc: gpu doesn't support YUV444 encode
[2026-03-23 10:45:54.106]: Error: NvEnc: NvEncUnregisterAsyncEvent() failed: NV_ENC_ERR_DEVICE_NOT_EXIST
[2026-03-23 10:45:54.139]: Info: Creating encoder [av1_nvenc]
[2026-03-23 10:45:54.140]: Info: Color coding: SDR (Rec. 709)
[2026-03-23 10:45:54.140]: Info: Color depth: 10-bit
[2026-03-23 10:45:54.140]: Info: Color range: JPEG
[2026-03-23 10:45:54.187]: Info: NvEnc: created encoder AV1 P1 async 10-bit two-pass rfi
[2026-03-23 10:45:54.230]: Info: 
[2026-03-23 10:45:54.230]: Info: // Ignore any errors mentioned above, they are not relevant. //
[2026-03-23 10:45:54.230]: Info: 
[2026-03-23 10:45:54.230]: Info: Found H.264 encoder: h264_nvenc [nvenc]
[2026-03-23 10:45:54.230]: Info: Found HEVC encoder: hevc_nvenc [nvenc]
[2026-03-23 10:45:54.230]: Info: Found AV1 encoder: av1_nvenc [nvenc]
[2026-03-23 10:45:54.230]: Info: Executing [Desktop]
[2026-03-23 10:45:54.294]: Info: New streaming session started [active sessions: 1]
[2026-03-23 10:45:54.408]: Info: nvprefs: No need to modify application profile settings
[2026-03-23 10:45:54.408]: Info: nvprefs: No need to modify global profile settings
[2026-03-23 10:45:54.449]: Info: CLIENT CONNECTED
[2026-03-23 10:45:54.773]: Info: Virtual audio device will use 32-bit to match default device
[2026-03-23 10:45:54.785]: Info: Changed virtual audio sink format to [S32 48000 2.0]
[2026-03-23 10:45:54.795]: Info: Audio mixer format is 32-bit, 48000 Hz, no resampling needed
[2026-03-23 10:45:54.801]: Info: Audio capture format is [F32 48000 2.0]
[2026-03-23 10:45:54.802]: Info: Opus initialized: 48 kHz, 2 channels, 96 kbps (total), LOWDELAY
[2026-03-23 10:45:54.894]: Info: 
Device Description : NVIDIA GeForce RTX 5060
Device Vendor ID   : 0x000010DE
Device Device ID   : 0x00002D05
Device Video Mem   : 7895 MiB
Device Sys Mem     : 0 MiB
Share Sys Mem      : 16374 MiB
Feature Level      : 0x0000B100
Capture size       : 1920x1080
Offset             : 0x0
Virtual Desktop    : 1920x1080
[2026-03-23 10:45:54.894]: Info: Active GPU has HAGS enabled
[2026-03-23 10:45:54.894]: Info: Using realtime GPU priority
[2026-03-23 10:45:54.894]: Info: 
Colorspace         : DXGI_COLOR_SPACE_RGB_FULL_G22_NONE_P709
Bits Per Color     : 8
Red Primary        : [0.679688,0.30957]
Green Primary      : [0.206055,0.693359]
Blue Primary       : [0.151367,0.0546875]
White Point        : [0.313477,0.329102]
Min Luminance      : 0.5 nits
Max Luminance      : 270 nits
Max Full Luminance : 270 nits
[2026-03-23 10:45:54.897]: Info: Desktop resolution [1920x1080]
[2026-03-23 10:45:54.897]: Info: Desktop format [DXGI_FORMAT_B8G8R8A8_UNORM]
[2026-03-23 10:45:54.897]: Info: Display refresh rate [59.934Hz]
[2026-03-23 10:45:54.897]: Info: Requested frame rate [60/1 exactly 60 fps]
[2026-03-23 10:45:54.897]: Info: Creating encoder [hevc_nvenc]
[2026-03-23 10:45:54.897]: Info: Color coding: SDR (Rec. 709)
[2026-03-23 10:45:54.898]: Info: Color depth: 8-bit
[2026-03-23 10:45:54.898]: Info: Color range: MPEG
[2026-03-23 10:45:54.915]: Info: Capture format [DXGI_FORMAT_B8G8R8A8_UNORM]
[2026-03-23 10:45:54.946]: Info: NvEnc: created encoder HEVC P1 async two-pass rfi
[2026-03-23 10:45:54.947]: Info: Minimum FPS target set to ~30fps (33.3333ms)
[2026-03-23 10:46:09.070]: Info: CLIENT DISCONNECTED
[2026-03-23 10:46:09.089]: Info: Starting async encoder teardown
[2026-03-23 10:46:09.118]: Info: Async encoder teardown complete

Online logs

No response

[aliefe04]

Proposed Solution

This issue occurs because Sunshine uses the packet size requested by the Moonlight client without validating it against the host's actual interface MTU. With VirtIO adapters, the reported link speed (10G) can cause Moonlight to request large packets (>10k) that exceed the actual MTU (1500).

Suggested fix: Add a configurable packet_size option to manually override the client's requested packet size. This would:

1. Add a new config option in stream section (e.g., packet_size = 0 where 0 = use client value, otherwise clamp to specified max)
2. Clamp config.packetsize in rtsp.cpp after receiving the client's value
3. Log a warning when the configured packet size differs from the client's request

This approach:

• ✅ Works around VirtIO MTU reporting quirks
• ✅ Doesn't require platform-specific MTU detection
• ✅ Gives users control for other edge cases (VPNs, tunnels, etc.)

I'd be happy to submit a PR for this if the maintainers agree with the approach.