Zyxel NBG-418N v2 - Инструкция по эксплуатации - Страница 110

Chapter 10 Network Address Translation

NBG-418N v2 User’s Guide

110

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.

Fig ure  7 9    

Multiple Servers Behind NAT Example

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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 NBG-418N v2 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 NBG-
418N v2's WAN port receives a response with a specific port number and protocol ("incoming" port), the 
NBG-418N v2 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.

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The following is an example of trigger port forwarding.

Fig ure  8 0    

Trigger Port Forwarding Process: Example

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