ZyXEL Communications NBG4115 User Manual

Chapter 11 NAT

User’s Guide

• Use  the  General (

) screen to enable NAT and set a 

default server.

• Use  the  Application (

) screen to change your 

NBG4115’s port forwarding settings.

• Use  the  Advanced (

) screen to change your 

NBG4115’s trigger port settings.

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

This denotes where a host is located relative to the NBG4115, 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.

Table 45   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.