WCF: Could not connect to net.tcp://... after patching Win10 2004

Mei Song Hu 1

Hello All, I got a strange issue about the WCF after patching Win 10 2004 update.

We implemented an application based on WCF+IIS, customer works well based on Win 10 1904 version, but it doesn't work after upgrading to 2004. In customer log, it says:

System.ServiceModel.EndpointNotFoundException: Could not connect to net.tcp://ecs-xxx/tcpbuffer. The connection attempt lasted for a time span of 00:00:21.0529749. TCP error code 10060: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 10.39.164.62:808.

But I can use this command sucessfully to access it: svcutil.exe http://xxx/xxx/ModelService.svc?wsdl

Customer client OS ver is Win 10 (2004) + .net48 .
The service is Windows Server 2019 (1809) + .net47.
There is no any change on service side.

More info about service side, the Client also works well when installing our services on Windows Server 2012 R2 + .net45 even client OS patched to 2004.

What I have tried?

In https://devblogs.microsoft.com/dotnet/net-framework-july-2020-cumulative-update-preview-for-windows-10-version-2004/, it says:
WCF2
When using a UPN Windows username with the format similar to username@乃士董 .domain in the username property of a NetworkCredential when using NetTcpBinding or NetNamedPipeBinding, WCF would incorrectly split the username and dns.domain placing them into the UserName and Domain properties. This is invalid in some scenarios and would result in failing to authenticate. This fix removes the credential modification when using a UPN username. The modification can be re-enabled by setting the AppSetting “wcf:enableLegacyUpnUsernameFix” to true.
Our case should not be related to it.

More clues: telnet command failed:

Microsoft Telnet> o 10.39.164.62 808

Connecting To 10.39.164.62...Could not open connection to the host, on port 808: Connect failed
But another client without 2004 update can use this command successfully.

Peng Ding-MSFT 96 Reputation points

2020-09-21T05:39:19.68+00:00

This is most likely a firewall problem. TCP error 10060 is the result of packet being dropped, not denied, so you need to check the firewall.
Mei Song Hu 1 Reputation point

2020-09-21T10:16:04.737+00:00

@PengDing , thanks for your reply, do you mean it is client firewall or host filewall? I can use the same command to access same host in another machine.
Peng Ding-MSFT 96 Reputation points

2020-09-22T01:18:39.33+00:00

You need to check the firewall on the server side. I suggest you turn off both the server side firewall and the client side firewall before testing.
Mei Song Hu 1 Reputation point

2020-09-22T01:40:42.737+00:00

@PengDing , thanks for your help, It cannot explain why I connected the same server successfully from another client without patching 2004 update if there is some firewall settings wrong on server side.

Meanwhile, that machine who patched 2004 also can execute telnet command successfully for another server (based on windows 2012 R2), and WCF services also work well when using that server.

I guess it is related to .net framework, but I have not seen related event abnormal logs on both client / server side. So far, the facts are there is no problem if the server installed .net 3.5 or 4.0,
Peng Ding-MSFT 96 Reputation points

2020-09-23T02:59:10.173+00:00

I also think this is related to the .net framework version. According to the update preview provided by Microsoft, I found that the nettcpbinding of wcf was updated in the win 10 2004 update. This update may cause authentication failure.
Mei Song Hu 1 Reputation point

2020-09-23T03:35:43.45+00:00

Yes，that was I already mentioned in the begining of my question. From the description it is related to user name format (username@乃士董 .domain).
In my case, it should not be related to it.
1）We don't use user@乃士董 .domain when logging on that machine;
2) I tried to add wcf:enableLegacyUpnUsernameFix=true in client app settings, it did not solve it.

Of course it may touch some things behind we don't know.

Another tricky things is I did not get any event logs for this error in both client and server, that make me paints because I have no direction on this issue.
Peng Ding-MSFT 96 Reputation points

2020-09-23T05:13:39.01+00:00

We will try to reproduce your problem. Can you provide partial configuration information about your service?
Mei Song Hu 1 Reputation point

2020-09-23T08:23:56.2+00:00

Sure，what info do you need? In fact, I think it is not related to our service. I think if I make telnet command work correctly in client and service. The issues should be solved.
Peng Ding-MSFT 96 Reputation points

2020-09-24T01:27:28.343+00:00

Configuration information about the service, such as what binding is used and the configuration of the binding.

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WCF: Could not connect to net.tcp://... after patching Win10 2004

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