PC Port Forwarding

Technical Specifications

Summary

PC-only TCP/UDP port forwarding (translation) and reflection that is transparent to any application on the OS. Unlike other software, PC Port Forwarding performs all operations on a Windows® PC without requiring additional hardware or complicated setups. This application operates automatically with high performance and features an intuitive user interface.

Port Forwarding Overview

Port forwarding is similar to network address translation (NAT), but it only translates port numbers. To illustrate, two computers on the Internet communicating via TCP/IP or UDP/IP use ports to identify their respective connection points. To communicate, each computer must know the other's IP address and port number. PC Port Forwarding forwards these ports so that when one computer sends data to a specific port, the data is transparently sent to a different port. Applications are unaware of this forwarding.

An example scenario for incoming port forwarding is as follows: When a remote computer sends traffic to the local computer on a specific port (e.g., HTTP port 80), PC Port Forwarding can be configured to remap the destination port 80 to a user-specified port (e.g., port 8080). As a result, any application on the local computer listening on port 8080 will receive the data from the remote computer that originally sent it to port 80.

Traffic Reflection Overview

In addition to port forwarding, PC Port Forwarding can perform traffic reflection, but this is limited to outgoing traffic. When an application on the local computer sends data to a remote server, PC Port Forwarding forwards the ports and loops all data back to the local computer. This allows the sending application to communicate with another application on the same computer, under the impression that it is communicating with a remote server.

It is important to note that even though traffic reflection loops traffic back to the local computer, the remote server must still have an IP address that is reachable from the local computer. In other words, the local computer must be able to determine the appropriate route for sending data to the remote server. Consequently, if the remote server is on the same subnet as the local computer, that remote server must be running to confirm that its IP address is directly reachable. This requirement does not apply to remote servers on other subnets that are reachable via a gateway.

An example scenario for traffic reflection is as follows: When an application (e.g., a web browser) on the local computer sends a request to port 80 of a remote server, PC Port Forwarding forwards the port and loops the data back to, for example, local port 8111. If the local computer has a web server or another application listening on port 8111, the web browser will communicate with that local web server instead of the remote one. The web browser will not know it is communicating with the local web server. For multi-homed computers, reflection will send the traffic back to the IP address from which it originated.

Working with PC Port Forwarding

The operation of PC Port Forwarding is based on rules that can be added and removed from the table in the main window. Adding, removing, or editing rules can be done via the Action menu or by right-clicking on the table.

PC Port Forwarding uses the destination port as a basis for internal port forwarding calculations. The destination port range is displayed in the table in the “Dst Port Range” column and tells PC Port Forwarding which ports to forward. For outgoing traffic, the destination port range is a range of ports on the remote server. For incoming traffic, the destination port range is on the local computer. The resulting port(s) after translation are displayed in the “Translate to Port(s)” column. The port range can be forwarded to a single port (merge operation) or to another port range (shift operation). For the translation of a port range into a single port, 'Translate to Port(s)' specifies the port to which all ports from the range are forwarded. For forwarding a port range to another port range, 'Translate to First Port' specifies the lowest port of the range to translate to.

Once all necessary rules are created, they need to be submitted to the remapping engine using the Apply button. To stop already applied rules from performing their function, submit an empty table or a table with all rules disabled. Whenever a new set of rules is applied, the previous one is discarded from the remapping engine.

Adding and editing rules is as simple as 1-2-3. First, a new rule needs to be added using the Action menu. Then, its properties need to be edited.

• Every rule has a unique ID that is assigned automatically when the rule is created. It cannot be changed.

• Each rule can be enabled or disabled. Disabled rules have no effect. All rules are created as disabled.

• Traffic Direction indicates which traffic direction to analyze when looking for the Dst Port Range. When a connection is initiated from the local computer to an external server, it is outgoing. When a remote computer accesses the local computer, it is incoming.

• Dst Port Range specifies the destination port range to analyze. When the traffic is incoming (from a remote computer), the destination port range is on the local computer. For outgoing traffic, the destination port range is on the remote server.

• Translate to First Port specifies the first port that the lowest port from the Dst Port Range will become after port forwarding is performed.

• Translated Coverage specifies the forwarding of a range of ports to a Single Port (merging) or to a Port Range (shifting).

• Finally, Traffic Reflection can be either enabled or disabled. For simple port forwarding (when a reversal in traffic direction is not needed), it should be disabled. If it is enabled, the outgoing traffic from the local computer will be routed back to the local computer without ever hitting the actual network.

PC Port Forwarding offers notifications for forwarding and reflection actions. Notifications are issued only once during connection establishment. After changing notification settings, rules need to be reapplied by clicking the Apply button.

The created set of rules can be saved to or loaded from a file.

Tutorial Video

Notes:
* Windows^® is a registered trademark of the Microsoft Corporation.