ZyXEL nbg-4615 사용자 가이드

 Chapter 19 NAT

NBG4615 User’s Guide

addresses and the ISP assigns the WAN IP address. The NAT network appears as a 
single host on the Internet.

Figure 106   Multiple Servers Behind NAT Example

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 NBG4615 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 NBG4615's WAN port 
receives a response with a specific port number and protocol ("incoming" port), 
the NBG4615 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.