Serial port redirection via an RDP connection is not working from a W10 PC to Windows Server 2019, but it is working from the same PC to Windows Server 2012

Question

I have a PC that has a weight scale (for weighing heavy raw materials) that is connected to the COM port. On this PC there is a shortcut for an RDP connection. This RDP shortcut has the "port" redirection checkbox checked under "local resources". This shortcut connects to a Windows Server 2012 server and passes the COM data just fine. On the server I can connect to COM1 using Putty and see data. Also, if from the CMD line I run: change port /query I see the following:

AUX = \DosDevices\COM1

COM1 = \Device\RdpDrPort;COM1:179\tsclient\COM1

This result only appears when the COM port is being successfully redirect. I am using Putty and the CMD line to remove the application on the server and to simplify testing.

PROBLEM: I have a second RDP shortcut that connects to a Windows Server 2019 server. This server will eventually replace the 2012 one. The RDP connection is successful, except that the COM port data is not being passed over from the PC. When I try to open the COM port using Putty I get: "Unable to open connection to COM1. Opening '.\COM1' Error 2: The system cannot find the file specified." And when I run change port /query, I just get: AUX = \DosDevices\COM1

I verified that there is not a GPO disabling redirection. Also, neither the 2012 server nor the 2019 server have a Ports section under Device Manager, yet the 2012 server is working. Virtual COM port software is not installed on the 2012 server.

Answer 1

Hello Shane Here are a few suggestions:

1. Group policy /registry has a higher priority than the UI settings, so please check in your server 2019 if there is any group policy settings / registry. In your condition, you can try to deploy a redirection in GP , so that ensure it will cover all lower settings.
2. When you use rdp advance settings to direct to a terminal server , there may be some devices have strange behaviour(they will direct to different COM port). So you may try if other COM port is fine.
3. Confirm if there is any error / warning in your eventlog(application, system) I hope this helps! Please let me know if you need any further assistance.

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Answer 2

Hi Karlie, thank you for your response. Below are the things I have looked into and tried, the first 3 are responses to your questions.

1. For the GPO, I set "Do not allow COM port redirect" to Disabled, which should force it to be allowed. I was set to Not Configured originally.
   • Computer Config -> Administrative Templates -> Windows Components -> Remote Desktop Services -> Remote Desktop Session Host -> Device and Resolution Redirection -> Do not allow COM port redirection 
2. We have tried a different COM port on the same PC and a different PC altogether. We also tried a serial-to-USB adapter. Those tests all worked fine with the Windows 2012 Server, but not on the 2019 Server. We also tried a different Windows 2019 server, with no success. I found some errors in the Event Viewer under RemoteDesktopServices-RdpCoreTS. These errors occur regardless if port redirection is enabled or not. In any case, I researched them, made the suggested GP/Registry changes, but still no sucess. Here is the location and the errors: Microsoft -> Windows -> RemoteDesktopServices-RdpCoreTS  Here they are in order in which they are received  Warning: The network characteristics detection function has been disabled because of Reason Code: 2(Server Configuration)..  Error: 'Failed GetConnectionProperty' in CUMRDPConnection::QueryProperty at 2884 err=[0x80004001]  Error: 'Connection doesn't support logon error redirector' in CUMRDPConnection::GetLogonErrorRedirector at 4179 err=[0x80004001]  Error: 'Failed CreateVirtualChannel call on this Connections Stack' in CUMRDPConnection::CreateVirtualChannel at 2498 err=[0xd0000001]  Error: 'Failed GetConnectionProperty' in CUMRDPConnection::QueryProperty at 2884 err=[0x80004001] 
3. The log on the local firewall (Defender) is turned on. There are no Denies. But even so, I temporarily disabled Defender, tried again with no success.   On the network firewall, there was an error that occurred during the RDP connection, but it has been corrected, the connection is now error and deny free, but still no success. 

Answer 3

Hi Shane,

were you able to solve the issue?

EDIT: Whoever may also experience this issue - check your print spooler service. The port redirection has dependencies to it and requires it to be running on the Target Server/Client you are connecting to.