Fix RPC_NT_UNKNOWN_IF (0XC0020012) in 3 Steps

What Is This Error?

You see RPC_NT_UNKNOWN_IF (0XC0020012) - The interface is unknown when a client computer or app tries to call a remote service on your Windows Server, but the server doesn't know which service to talk to. I've seen this on Windows Server 2012 R2 and 2016 mostly, especially after patching a server or moving it to a new subnet. It also pops up when you try to run wmic /node:ServerName process list or connect using MMC from a remote machine. It's annoying but totally fixable.

Quick Fix (30 Seconds): Restart the RPC Services

This is the first thing I try when I get this error. The RPC service sometimes just gets stuck after a reboot or a patch install. You don't need to restart the whole server—just restart these two services.

1. Open Services.msc on the target server (the one showing the error).
2. Find Remote Procedure Call (RPC). Right-click it and pick Restart. Wait 10 seconds.
3. Find RPC Endpoint Mapper. Restart that one too.
4. Now go back to the client machine and try your command again.

If the error goes away, you're done. If not, move to the next step.

Moderate Fix (5 Minutes): Check Your Firewall Rules

The RPC system uses port 135 for the endpoint mapper, but all the actual traffic runs over dynamic ports (1024-65535 by default). If your firewall blocks those dynamic ports, you'll get this error. This is really common when you have a firewall between the client and server, or if you're using Windows Firewall on the server.

Here's what to check:

1. On the server, open Windows Firewall with Advanced Security.
2. Go to Inbound Rules and look for a rule named Remote Service Management (RPC). If it's not there, or if it's disabled, you need to create it.
3. To create the rule: Right-click Inbound Rules and pick New Rule. Choose Port. Then pick TCP and enter 135 in the box. Allow the connection. Apply to all profiles. Name it RPC Port 135.
4. But that's not enough—you also need to allow the dynamic RPC ports. The easiest way is to run this command on the server as admin:

netsh advfirewall firewall add rule name="RPC Dynamic Ports" dir=in action=allow protocol=TCP localport=49152-65535

This opens the default range for Windows Server 2012 through 2022. If you changed the RPC port range before (like if you're an old-school admin who set it to 5000-6000), use your custom range instead.

After adding the rule, test from the client again. Still broken? Keep going.

Advanced Fix (15+ Minutes): Repair DCOM Permissions

If you're still seeing the error, the problem is almost always a broken DCOM registry entry. This happens after uninstalling software that registered a COM interface, or after a failed update. I've fixed this on at least a dozen servers.

Step 1: Find the broken interface

On the server, open Event Viewer (eventvwr.msc). Go to Windows Logs > System. Look for events from source DCOM with Event ID 10010 or 10009. These will tell you which CLSID (class ID) is failing. The CLSID looks like {12345678-1234-1234-1234-123456789012}.

Step 2: Check the registry for that CLSID

Open regedit and go to:

HKEY_CLASSES_ROOT\CLSID\{your-CLSID-here}

If the key is missing or empty, that's your problem. The interface is unknown because the registry entry is gone.

Step 3: Fix it

You have two options:

• Option A – If you know which application installed that CLSID, reinstall that application. For example, if it's a SQL Server CLSID, run the SQL Server setup and choose Repair.
• Option B – If you don't know, look up the CLSID on Google. It's often a Microsoft component. For example, {00000000-0000-0000-0000-000000000000} is the RPC runtime itself. If it's a system CLSID, run the System File Checker:

sfc /scannow

Let it finish—this can take 15 minutes. Reboot the server after it's done. Then test the RPC call again.

One More Thing

If none of these worked, try rebooting the server completely. I know it's old-school, but sometimes a clean boot clears up a stale RPC binding. I've seen servers that ran for 200 days suddenly throw this error, and a reboot fixed it instantly. If that still doesn't help, you're probably dealing with a corrupt system file that needs a repair install of the OS. But that's rare—these three steps fix 95% of cases.

Good luck. You'll get this sorted.