P-660HN-51 User’s Guide
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CHAPTER 8
Network Address Translation
(NAT)
8.1 Overview
This chapter discusses how to configure NAT on the Zyxel Device. 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 to configure forward incoming service requests to the server(s) on your
local network (Section 8.2 on page 110).
• Use the Applications screen to forward incoming service requests to the server(s) on your local
network (Section 8.3 on page 113).
• Use the Port Triggering screen to add and configure the Zyxel Device’s trigger port settings (Section
8.4 on page 114).
• Use the DMZ screen to configure a default server (Section 8.5 on page 117).
• Use the ALG screen to enable and disable the SIP (VoIP) ALG in the Zyxel Device (Section 8.6 on
page 118).
• Use the Sessions screen to limit the number of concurrent NAT sessions all clients can use (Section 8.7
on page 118).
8.1.2 What You Need To Know
Inside/Outside
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
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
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