Network Address Translation (NAT)
Port Forwarding
Use Port Forwarding to forward incoming service requests from the Internet to the servers on your local network. Port forwarding is commonly used when you want to host online gaming, P2P file sharing, or other servers on your network.
You may enter a single port number or a range of port numbers to be forwarded, and the local IP address of the desired server. The port number identifies a service; for example, web service is on port 80 and FTP on port 21. In some cases, such as for unknown services or where one server can support more than one service (for example both FTP and web service), it might be better to specify a range of port numbers. You can allocate a server IP address that corresponds to a port or a range of ports. Please refer to RFC 1700 for further information about port numbers.
*Many residential broadband ISP accounts do not allow you to run any server processes (such as a Web or FTP server) from your location. Your ISP may periodically check for servers and may suspend your account if it discovers any active services at your location. If you are unsure, refer to your ISP.
Configure Servers Behind Port Forwarding (Example)
Let's say you want to assign ports 21-25 to one FTP, Telnet and SMTP server (A in the example), port 80 to another (B in the example), a default server IP address of 192.168.1.35 to a third (C in the example), and a default server IP address of 192.168.1.36 to a fourth (D in the example). You assign the LAN IP addresses and the ISP assigns the WAN IP address. The NAT network appears as a single host on the Internet.
Multiple Servers Behind NAT Example
Port Forwarding
Click Network Setting > NAT to open the Port Forwarding screen.
*TCP port 7547 is reserved for system use.
Network Setting > NAT > Port Forwarding
The following table describes the fields in this screen.
Network Setting > NAT > Port Forwarding 
LABEL
Description
Add New Rule
Click this to add a new port forwarding rule.
#
This is the index number of the entry.
Status
This field indicates whether the rule is active or not.
A yellow bulb signifies that this rule is active. A gray bulb signifies that this rule is not active.
Service Name
This is the service’s name. This shows User Defined if you manually added a service. You can change this by clicking the edit icon.
Originating IP
This is the source’s IP address.
WAN Interface
Select the WAN interface for which to configure NAT port forwarding rules.
Server IP Address
This is the server’s IP address.
Start Port
This is the first external port number that identifies a service.
End Port
This is the last external port number that identifies a service.
Translation Start Port
This is the first internal port number that identifies a service.
Translation End Port
This is the last internal port number that identifies a service.
Protocol
This field displays the protocol (TCP, UDP, TCP+UDP) used to transport the packets for which you want to apply the rule.
Modify
Click the Edit icon to edit the port forwarding rule.
Click the Delete icon to delete an existing port forwarding rule. Note that subsequent address mapping rules move up by one when you take this action.
Add or Edit Port Forwarding
Create or edit a port forwarding rule. Specify either a port or a range of ports, a server IP address, and a protocol to configure a port forwarding rule. Click Add New Rule in the Port Forwarding screen or the Edit icon next to an existing rule to open the following screen.
Network Setting > NAT > Port Forwarding: Add or Edit
*To configure port forwarding, you need to have the same configurations in the Start Port, End Port, Translation Start Port, and Translation End Port fields.
To configure port translation, you need to have different configurations in the Start Port, End Port, Translation Start Port, and Translation End Port fields.
Here is an example to configure port translation. Configure Start Port to 100, End Port to 120, Translation Start Port to 200, and Translation End Port to 220.
*TCP port 7547 is reserved for system use.
The following table describes the labels in this screen.
Network Setting > NAT > Port Forwarding: Add or Edit 
Label
Description
Active
Click to turn the port forwarding rule on or off.
Service Name
Enter a name for the service to forward. You can use up to 256 printable characters except [ " ], [ ` ], [ ' ], [ < ], [ > ], [ ^ ], [ $ ], [ | ], [ & ], or [ ; ]. Spaces are allowed.
WAN Interface
Select the WAN interface for which to configure NAT port forwarding rules.
Start Port
Configure this for a user-defined entry. Enter the original destination port for the packets.
To forward only one port, enter the port number again in the End Port field.
To forward a series of ports, enter the start port number here and the end port number in the End Port field.
End Port
Configure this for a user-defined entry. Enter the last port of the original destination port range.
To forward only one port, enter the port number in the Start Port field above and then enter it again in this field.
To forward a series of ports, enter the last port number in a series that begins with the port number in the Start Port field above.
Translation Start Port
Configure this for a user-defined entry. This shows the port number to which you want the Zyxel Device to translate the incoming port. For a range of ports, enter the first number of the range to which you want the incoming ports translated.
Translation End Port
Configure this for a user-defined entry. This shows the last port of the translated port range.
Server IP Address
Enter the inside IP address of the virtual server here.
Configure Originating IP
Click the Enable checkbox to enter the source IP in the next field.
Originating IP
Enter the source IP address here.
Protocol
Select the protocol supported by this virtual server. Choices are TCP, UDP, or TCP/UDP.
OK
Click this to save your changes.
Cancel
Click this to exit this screen without saving.