Nat Port Forwarding Example; Trigger Port Forwarding; Trigger Port Forwarding Example - ZyXEL Communications LTE3311 series User Manual

10.6.2 NAT 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) and assign a default server IP address of 192.168.1.35 to a
third (C 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.
Figure 61 Multiple Servers Behind NAT Example

10.6.3 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 LTE3311 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
LTE3311's WAN port receives a response with a specific port number and protocol ("incoming"
port), the LTE3311 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.

10.6.4 Trigger Port Forwarding Example

The following is an example of trigger port forwarding.
Chapter 10 NAT
LTE3311 Series User's Guide
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