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WebShare 141W
A02-RA141-W54 Pag. 47
CHAPTER 7: Network Address Translation
(NAT)
This chapter discusses how to configure NAT on the WebShare Wireless Router
ADSL2+.
7.1 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.
7.1.1 NAT Definitions
Inside/outside denotes where a host is located relative to the ADSL Router, 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.
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.
7.1.2 What NAT Does
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)