Kestrel unable to start

Question

When specifying a port to bind to with .UseKestrel() I get the errors listed below.. but if I remove the kestrel options everything works normally if I check the API from my browser.

I've tried binding to the port that my application defaults to with no ports chosen and I've tried checking netstat to actively avoid any ports that are in use. Nothing works but removing the options entirely. This is not replicated on my Mac or another Windows 10 machine. This device is Windows 10.

.UseKestrel(options =>
{
    options.Listen(IPAddress.Loopback, 50470);
    options.Listen(IPAddress.Any, 80);
})

: Microsoft.AspNetCore.Server.Kestrel[0]
Overriding address(es) 'http://localhost:50470/'. Binding to endpoints defined 
in UseKestrel() instead.
crit: Microsoft.AspNetCore.Server.Kestrel[0]
Unable to start Kestrel.
System.Net.Sockets.SocketException (10013): An attempt was made to access a 
socket in a way forbidden by its access permissions
at 
System.Net.Sockets.Socket.UpdateStatusAfterSocketErrorAndThrowException
(SocketError error, String callerName)
at System.Net.Sockets.Socket.DoBind(EndPoint endPointSnapshot, SocketAddress 
socketAddress)
at System.Net.Sockets.Socket.Bind(EndPoint localEP)
at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketTransport.
BindAsync() at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServer. 
<>c__DisplayClass21_01.<<StartAsync>g__OnBind|0>d.MoveNext() ` 

Answer 1

Also check Darkthread's answer here: https://superuser.com/questions/1486417/unable-to-start-kestrel-getting-an-attempt-was-made-to-access-a-socket-in-a-way

We discovered that a port we had been using for a long time wasn't acccessible anymore because it had been reserved by Windows! You may wish to check reserved ports using this command: netsh interface ipv4 show excludedportrange protocol=tcp

Answer 2

The additional binding of port 80 in ".UseKestrel(options => { options.Listen(...) })" was causing the issue in my case.