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P-2612HNU-Fx User’s Guide
149
CHAPTER 8
Network Address Translation
(NAT)
8.1 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 What You Can Do in this Chapter
Use the Port Forwarding screen (Section 8.2 on page 150) to configure forward
incoming service requests to the server(s) on your local network.
8.1.2 What You Need To Know
The following terms and concepts may help as you read this chapter.
Inside/Outside and Global/Local
Inside/outside denotes where a host is located relative to the ZyXEL Device, 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.
NAT
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,