ZyWALL 10/50 Internet Security Gateway

Chapter 9

Network Address Translation (NAT)

This chapter discusses how to configure NAT on the ZyWALL.

9.1Introduction

NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a host in a packet, e.g., the source address of an outgoing packet, used within one network to a different IP address known within another network.

9.1.1 NAT Definitions

Inside/outside denotes where a host is located relative to the ZyWALL, e.g., the workstations 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, e.g., 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.

 

Table 9-1 NAT Definitions

TERM

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.

 

 

NAT

9-1