ZyXEL Communications Corporation NBG4104 Manual De Usuario

Chapter 13 NAT

NBG4104 User’s Guide

• Use  the  General screen to enable NAT and set a default server (

• Use  the  Application screen to change your NBG4104’s port forwarding settings (

).

The following terms and concepts may help as you read through this chapter.

This denotes where a host is located relative to the NBG4104, for example, the computers of your 
subscribers are the inside hosts, while the web servers on the Internet are the outside hosts. 

This denotes the IP address of a host in a packet as the packet traverses a router, for example, the 
local address refers to the IP address of a host when the packet is in the local network, while the 
global address refers to the IP address of the host when the same packet is traveling in the WAN 
side. 

Note: Inside/outside refers to the location of a host, while global/local refers to the IP 

address of a host used in a packet. 

An inside local address (ILA) is the IP address of an inside host in a packet when the packet is still 
in the local network, while an inside global address (IGA) is the IP address of the same inside host 
when the packet is on the WAN side. The following table summarizes this information.

Note: NAT never changes the IP address (either local or global) of an outside host.

In the simplest form, NAT changes the source IP address in a packet received from a subscriber 
(the inside local address) to another (the inside global address) before forwarding the packet to the 
WAN side. When the response comes back, NAT translates the destination address (the inside 

NAT Definitions

Inside

This refers to the host on the LAN.

Outside

This refers to the host on the WAN.

Local

This refers to the packet address (source or 
destination) as the packet travels on the LAN.

Global

This refers to the packet address (source or 
destination) as the packet travels on the WAN.