How to Buy print this page print

Port Triggering on Routers

Article ID: 2830


Port triggering is a configuration option which is similar to port forwarding on a NAT-enabled router. It allows a host machine to dynamically forward traffic to a specific port and allows traffic to come back to the host. The purpose of this article is to explain what port triggering is and how it works.

Applicable Devices

What is Port Triggering and How Does It Work?

Port triggering is very similar to port forwarding. Port forwarding is the organizational process of sending data through a router. Port triggering is the same as port forwarding with an addition of a switch to each port. The switch is turned on or off by the data flowing out of a port. Port Triggering is more secure than port forwarding because the incoming ports are not open all the time like they are in port forwarding. In port triggering, ports are open when a program is actively using the port, otherwise they will be closed. Any computer on a network can use the port triggering setup since it does not require an internal IP address to forward the incoming ports. If more than one user tries to access it, there will be problems. Below is a good example of port triggering.

Suppose there is a port triggering configuration that has already been set up.

1. The configuration says that when data gets sent out of port 40 it gets sent to port 70. This normally happens between a computer and a router.

2. The router notices that the traffic has exited port 40 from the computer and refers to the configuration as to what to do with the data.

3. The data then gets sent to port 70 of the computer. Only one computer can forward port 70 at a time.

4. Data stops being sent out of port 40 while data is still being forwarded from port 70 for a predetermined amount of time.

The software requires ports to be forwarded at a constant rate. With that, port triggering is possible. If the software does not keep sending data out of port 40, then the router will close the incoming ports and that will disrupt any downloads being made. 

Still need help? Try Guide Me Troubleshooting!


© 2018 Cisco Systems, Inc. All rights reserved.