ZyXEL VSG-1200 User Manual download pdf (Page 74)

VSG-1200 V2 User’s Guide

Chapter 8 NAT Pool 74

CHAPTER 8

NAT Pool

This chapter shows how to configure Network Address Translation (NAT) on the WAN for

VPN packets.

8.1 NAT Overview

NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a

host in a packet, for example, the source address of an outgoing packet, used within one

network to a different IP address known within another network.

8.1.1 NAT Definitions

Inside/outside denotes where a host is located relative to the VSG, for example, the computers

of your subscribers are the inside hosts, while the web servers on the Internet are the outside

hosts.

Global/local 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 that inside/outside refers to the location of a host, while global/local refers to the IP

address of a host used in a packet. Thus, 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.

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

Table 11 NAT Definitions

ITEM DESCRIPTION

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.

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ZyXEL VSG-1200 User Manual Page 74