How to change the port number for Asp.Net core app?

Yes this will be accesible from other machines if you bind on any external IP address. For example binding to http://*:80 . Note that binding to http://localhost:80 will only bind on 127.0.0.1 interface and therefore will not be accesible from other machines.

Visual Studio is overriding your port. You can change VS port editing this file Properties\launchSettings.json or else set it by code:

        var host = new WebHostBuilder()
            .UseKestrel()
            .UseContentRoot(Directory.GetCurrentDirectory())
            .UseIISIntegration()
            .UseStartup<Startup>()
            .UseUrls("http://localhost:80") // <-----
            .Build();

        host.Run();

A step by step guide using an external config file is available here.

It's working to me.

I use Asp.net core 2.2 (this way supported in asp.net core 2.1 and upper version).

add Kestrel section in appsettings.json file. like this:

{
  "Kestrel": {
    "EndPoints": {
      "Http": {
        "Url": "http://localhost:4300"
      }
    }
  },
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "AllowedHosts": "*"
}

and in Startup.cs:

public Startup(IConfiguration configuration, IHostingEnvironment env)
{
      var builder = new ConfigurationBuilder()
         .SetBasePath(env.ContentRootPath)
         .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
         .AddEnvironmentVariables();

      Configuration = builder.Build();
}

In Asp.net core 2.0 WebApp, if you are using visual studio search LaunchSettings.json. I am adding my LaunchSettings.json, you can change port no as u can see.