Fix: Failed to bind to address

Here’s the quick fix for the exception: “Failed to bind to address https://localhost:xxxxx (System.IO.IOException)“.

net stop winnat
net start winnat

Note: Run as admin.

ref: https://stackoverflow.com/questions/71242005/failed-to-bind-to-localhost-invalid-exception-error-visual-studio-2022

The issue most likely is related to Kestrel failing to bind to a network address, which is often caused by a port conflict.

So if you’re sure there aren’t other applications that have claimed the particular port, restart the WinNAT service.

Update [dt. 2026-03-01]

I encountered this error again and it wasn’t as easy a fix this time when working on a .NET project with multiple start up projects. I have IIS Express and Kestrel launch profiles defined and I did for my curiosity switch between the two.

Btw, don’t use IIS Express if you have Kestrel or even IIS; no real point.

Okay back to the issue at hand…

Most common causes why the app cannot bind to http://localhost:xxxxx:

The port is in an excluded/reserved range.
Another process is already using the port.
HTTPS/SSL binding conflicts.

Practical fixes (in order)

1) (The above quick fix) Restart WinNAT service

Still the likeliest and quickest.

net stop winnat
net start winnat

Note: Run as admin.

2) Delete “applicationhost.config” inside the “.vs” folder

Magic of using IIS Express I believe: You’ll find an “applicationhost.config” here: <project root>\.vs\<project>.slnx\config\.

Delete that!

3) If possible, kill the process capturing the port

If applicable to you, stop IIS/IIS Express first and check if your app runs before proceeding.

Run this in an admin PowerShell or Command Prompt:

netstat -ano | findstr :xxxxx

If any line appears, note the PID and then:

tasklist | findstr <PID>

If a process owns the port, stop it and try again.

4) Check Windows excluded port ranges

Use this command to see reserved TCP ports:

netsh interface ipv4 show excludedportrange protocol=tcp

port exclusion ranges

If your port is excluded, Windows will reject binding.

You might want to try (step 8) Use a port outside those ranges or (step 7) reboot to clear some dynamic reservations.

5) Run elevated when HTTPS is enabled

If launchSettings.json includes https://localhost:xxxxx (or sslPort), try running elevated:

Right‑click Visual Studio (or dotnet run terminal) → Run as administrator.
This can unblock HTTPS binding on some ports.

6) Temporarily disable HTTPS in the profile

If HTTPS is not required immediately, simplify applicationUrl:

"applicationUrl": "http://localhost:xxxxx"

instead of:

"applicationUrl": "https://localhost:xxxxx;http://localhost:xxxxx"

This removes SSL/TLS binding for that port and often avoids the error.

7) Restart Visual Studio or Windows

If stale debug sessions are stuck, a clean restart can clear temporary conflicts/exclusions.

8) Give up, use a different port

It’s a pain to have to restart a PC in the middle of work.

Change the port your app listens on in Properties/launchSettings.json:

{
  "profiles": {
    "MyApp": {
      "commandName": "Project",
      "applicationUrl": "http://localhost:5000",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      }
    }
  }
}

Replace xxxxx with 5000 (or any unused port), restart, and verify. If it works, xxxxx is blocked/reserved.

refs: