Trigger Port Forwarding; Trigger Port Forwarding Example - ZyXEL Communications EMG6765-Q10A User Manual

Figure 64 Multiple Servers Behind NAT Example

13.5.3 Trigger Port Forwarding

Some services use a dedicated range of ports on the client side and a dedicated range of ports on the
server side. With regular port forwarding you set a forwarding port in NAT to forward a service (coming in
from the server on the WAN) to the IP address of a computer on the client side (LAN). The problem is that
port forwarding only forwards a service to a single LAN IP address. In order to use the same service on a
different LAN computer, you have to manually replace the LAN computer's IP address in the forwarding
port with another LAN computer's IP address.
Trigger port forwarding solves this problem by allowing computers on the LAN to dynamically take turns
using the service. The EMG6765-Q10A records the IP address of a LAN computer that sends traffic to the
WAN to request a service with a specific port number and protocol (a "trigger" port). When the
EMG6765-Q10A's WAN port receives a response with a specific port number and protocol ("incoming"
port), the EMG6765-Q10A forwards the traffic to the LAN IP address of the computer that sent the
request. After that computer's connection for that service closes, another computer on the LAN can use
the service in the same manner. This way you do not need to configure a new IP address each time you
want a different LAN computer to use the application.

13.5.4 Trigger Port Forwarding Example

The following is an example of trigger port forwarding.
Chapter 13 NAT
EMG6765-Q10A User's Guide
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