Port 135 (MS RPC)
Port 135 is the RPC Endpoint Mapper (IANA name epmap). Windows services such as WMI, DCOM and Active Directory first ask it which dynamic port to use, then connect there.
- Service
- MS RPC
- Protocol
- TCP
- IANA registry
- Officially assigned: epmap (DCE endpoint resolution), TCP/UDP
Check if a port is open on your IP
We only check the address you are visiting from, one TCP port at a time. You cannot enter someone else’s address: this is not a port scanner.
Is it safe to open port 135?
Port 135 belongs on internal Windows networks only. Block it at the internet edge: remote management over RPC from the internet is a common way into unpatched machines.
Sources
“Port 135 is already in use”: how to fix it
The error means another program is already listening on port 135. Find its process ID (PID), then stop that program or start yours on a different port.
Windows (Command Prompt or PowerShell as administrator)
netstat -ano | findstr :135taskkill /PID <PID> /FmacOS
lsof -nP -iTCP:135 -sTCP:LISTENkill <PID>Linux
sudo ss -ltnp | grep :135sudo lsof -i :135sudo kill <PID>Replace <PID> with the number from the last column (Windows) or the PID column (macOS, Linux).
Why a port can look closed when your server is running
Most home networks sit behind a router doing NAT: the router owns the public address, and your computer has a private one such as 192.168.1.10. A connection from the internet reaches the router and stops there unless you add a port forwarding rule to your computer.
Many mobile and some home providers go further and use carrier-grade NAT (CGNAT): several customers share one public address, and your router itself gets an address from 100.64.0.0/10. Then no rule on your side can open a port; ask the provider for a public IP or use a tunnel or VPN service.
Even with forwarding in place, the firewall on the computer (Windows Defender Firewall, ufw, firewalld) must allow the port, and the program must listen on all interfaces (0.0.0.0), not only on 127.0.0.1.
UDP cannot be checked this way: a UDP service usually stays silent to packets it does not understand, so “no answer” means nothing. This check uses TCP only.
Frequently asked questions
What is port 135 used for?
Port 135 is the RPC Endpoint Mapper (IANA name epmap). Windows services such as WMI, DCOM and Active Directory first ask it which dynamic port to use, then connect there.
Is port 135 TCP or UDP?
Port 135 uses TCP. IANA reserves the number for both TCP and UDP, but in practice only TCP is used.
Is it safe to open port 135?
Port 135 belongs on internal Windows networks only. Block it at the internet edge: remote management over RPC from the internet is a common way into unpatched machines.
How do I free port 135 if it is already in use?
Find the process: on Windows run netstat -ano | findstr :135 and stop it with taskkill /PID <pid> /F; on macOS or Linux run lsof -i :135 and stop it with kill <pid>.