netstat -na|find "3340"

Alternatively, you can check that the port is not listening locally using the PowerShell cmdlet Test-NetConnection:

Test-NetConnection -ComputerName localhost -Port 3340

Check the status of the service in the services.msc console or using the PowerShell command:

Get-Service iphlpsvc

IPv6 support must be enabled on the network interface for which the port forwarding rule is being created.

These are the prerequisites for the correct operation of port forwarding in Windows. Without the IP Helper service and without IPv6 support enabled, the port redirection won’t work.

To make port forwarding work on Windows Server 2003/XP, you must additionally set the IPEnableRouter parameter to 1 under the registry key HKEY_LOCAL_MACHINE\ System\CurrentControlSet\services\Tcpip\Parameter.

You can identify the process that is listening on the specified port by its PID (in our example, the PID is 636):

tasklist | findstr 636

Now try to connect to the new port from a remote computer using any RDP client. You need to specify 3340 as the RDP port number. It is specified after the colon following the RDP host address. For example, 10.10.1.110:3340

The RDP connection should be established successfully.

Portproxy port forwarding rules are permanent and are not cleared when you restart Windows. These rules are stored in the registry. You can list the netsh forwarding rules in the registry using PowerShell:

Get-ItemProperty -Path HKLM:\SYSTEM\CurrentControlSet\Services\PortProxy\v4tov4\tcp

If you want to forward an incoming TCP connection to a remote computer, use the following command:

netsh interface portproxy add v4tov4 listenport=3389 listenaddress=0.0.0.0 connectport=3389 connectaddress=192.168.100.101

This rule will redirect all incoming RDP traffic (from local TCP port 3389) from this computer to a remote host with an IP address 192.168.1.100.

Note that the portproxy mode in Windows doesn’t support saving the source IP in a forwarded network packet. Those, if you forward port 443 port from a Windows device to an internal web server, then all incoming connections will appear on the target server as coming from the same IP address (from your Windows host with netsh portproxy enabled). If you need to use source IP forwarding, you need to use NAT on an external firewall or on Hyper-V (described below).

Configuring Firewall Rules for Port Forwarding Mode in Windows

Ensure that your firewall (Microsoft Windows Defender or a third-party firewall, which is often part of the anti-virus software) allows incoming connections to the new port. You can add a new allow rule to Windows Defender Firewall with the command:

netsh advfirewall firewall add rule name="forwarded_RDPport_3340" protocol=TCP dir=in localip=10.1.1.110? localport=3340 action=allow

Or using the New-NetFirewallRule PowerShell cmdlet:
New-NetFirewallRule -DisplayName "forwarder_RDP_3340" -Direction Inbound -Protocol TCP –LocalPort 3340 -Action Allow

When creating an inbound firewall rule for TCP/3340 port via Windows Defender Firewall graphical interface, you don’t need to associate a program or process with the rule. This port is only listened on by the network driver.

If you disable the portproxy rule, be sure to remove the remaining firewall rule as follows:

netsh advfirewall firewall del rule name="RDP_3340"

or remove firewall rule with PowerShell:

Remove-NetFirewallRule -Name RDP_3340

Managing Netsh Port Forwarding Rules in Windows

You can create any number of port forwarding rules in Windows. All netsh interface portproxy rules are persistent and remain after a Windows restart.

To display a list of all enabled TCP port forwarding rules on Windows, run the command:

netsh interface portproxy show all

In our case, there is only one forwarding rule from local port 3340 to 3389:

Listen on ipv4:???????????? Connect to ipv4:
Address???????? Port??????? Address???????? Port
--------------- ----------? --------------- ----------
10.1.1.110???? 3340??????? 10.1.1.110???? 3389

#========================
# Port Proxy configuration
#========================
pushd interface portproxy
reset
add v4tov4 listenport=3340 connectaddress=10.1.1.110 connectport=3389
popd
# End of Port Proxy configuration

If you need to change the settings of an existing portproxy rule, use the following command:

netsh interface portproxy set v4tov4 listenport=3340 listenaddress=10.10.1.110?connectport=3300 connectaddress=10.10.1.110

In this example, we have changed the portproxy target port number to 3300.

To remove a specific port forwarding rule:

netsh interface portproxy delete v4tov4 listenport=3340 listenaddress=10.1.1.110

To remove all existing port mapping rules and completely clear the port forwarding rules table:

netsh interface portproxy reset

If you have WSL (Windows Subsystem for Linux) installed on your computer, you can create a simple PowerShell script to create a port forwarding rule to the WSL 2 virtual machine (a WSL2 VM has its own virtual ethernet adapter with a unique IP address):

wsl --shutdown;
netsh interface portproxy reset;
$wsl_ipaddr = wsl -d Ubuntu-20.04 hostname -I;
netsh interface portproxy add v4tov4 listenport=443 listenaddress=0.0.0.0 connectport=443 connectaddress=$wsl_ipaddr ;
netsh interface portproxy show all;
exit;

Another implicit feature of portproxy is the ability to make any remote network service look like it runs locally. For example, you want to forward the connections from local port 9090 to a remote HTTPS server (google.com:443)

netsh interface portproxy add v4tov4 listenport=9090 connectport=443 connectaddress=google.com protocol=tcp

Now, the Google search page will open if you go to http://localhost:9090/ in your browser (you need to ignore SSL_ERROR_BAD_CERT_DOMAIN errors). So despite the browser accessing the local computer address, it opens a page from an external web server.

Windows cannot forward a range of TCP ports. If you need to forward multiple ports, you will have to manually create multiple portproxy redirecting rules.

Port forwarding rules can also be used to redirect a port from the external IP address of a physical NIC to a port of a virtual machine running on the same host. In Hyper-V, you can configure port forwarding on a Virtual Switch level (see below).

Port Forwarding with NAT Rules on Hyper-V Virtual Switch

When using the Hyper-V role on your computer (it can be installed on both Windows 10/11 and Windows Server, or as a free Hyper-V Server), you can configure DNAT port forwarding rules using PowerShell. Suppose you want to redirect all HTTPS traffic that your Hyper-V host receives to the IP address of the virtual machine running on the host. To do this, use the Hyper-V StaticMapping commands.

Create a Hyper-V virtual switch:

New-VMSwitch -SwitchName NAT_Switch -SwitchType Internal

Set the IP address for the new virtual switch:

New-NetIPAddress?-IPAddress 192.168.100.1?-PrefixLength 24? -InterfaceAlias "vEthernet (NAT_Switch)"

Enable NAT for this network:

New-NetNat -Name NATNetwork -InternalIPInterfaceAddressPrefix 192.168.100.0/24

Connect the VM to your NAT_Switch and assign it a static IP address (for example, 192.168.10.80). Set the Hyper-V virtual switch IP address (192.168.100.1 in this case) as the default gateway for the virtual machine’s network connection.

You can now enable port forwarding from the Hyper-V host to the virtual machine:

Add-NetNatStaticMapping -NatName NATNetwork443?-Protocol TCP? -ExternalIPAddress 0.0.0.0/24? -ExternalPort 443? -InternalIPAddress 192.168.10.80? -InternalPort 443

After executing these PowerShell commands, all HTTPS traffic that comes to the TCP/443 port of the Hyper-V host will be forwarded to the private IP address of the virtual machine.

If you want to create a port forwarding rule for a non-standard port, don’t forget to open it in Windows Firewall:

New-NetFirewallRule -DisplayName "HyperV_Nat_444" -Direction Inbound -LocalPort 444 -Protocol TCP -Action Allow -Enabled True

You can display a complete list of NAT/PAT port forwarding rules on a Hyper-V host like this:

Get-NetNat