This repository contains projects for troubleshooting TCP connectivity issues we have experienced when running an ASP.NET Core 3.1 web application with VNet integration for accessing Azure VMs in our cloud infrastructure.
We have had no problems with .NET Core 2.x applications, but .NET Core 3.1 apps throw an exception from TcpClient.Connect() stating "An attempt was made to access a socket in a way forbidden by its access permissions."
The solution contains the following projects:
- EchoServer: A simple TCP echo server (.NET Framework 4.6.2), intended to be run on an Azure virtual machine.
- EchoClient: A .NET Standard 2.0 library with a Test() method that connects to the echo server, sends "Hello world!" over the network, and then closes the connection.
- Two ASP.NET Core web applications (a .NET Core 2.1 version and a .NET Core 3.1 version), intended to be run in as Azure App Services with VNET integration to connect to the EchoServer VM. These two web apps are boilerplate projects, except their Home Controllers try to use the EchoClient library to connect to the EchoServer service.