Nat; Chapter 10 Nat; Overview; What You Can Do - ZyXEL Communications LTE3301-M209 User Manual

10.1 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 is changed to
a different IP address known within another network.
The figure below is a simple illustration of a NAT network. You want to assign ports 21-25 to one FTP, Telnet
and SMTP server (A in the example), port 80 to another (B in the example) and assign a default server IP
address of 192.168.1.35 to a third (C in the example).
You assign the LAN IP addresses to the devices (A to D) connected to your Zyxel Device. The ISP assigns
the WAN IP address. The NAT network appears as a single host on the Internet. All traffic coming from A
to D going out to the Internet use the IP address of the Zyxel Device, which is 192.168.1.1.
Figure 56 NAT Example
Note: You must create a firewall rule in addition to setting up NAT, to allow traffic from the
WAN to be forwarded through the Zyxel Device.

10.1.1 What You Can Do

• Use the General screen to enable NAT
• Use the Port Forwarding screen to set a default server and change your Zyxel Device's port forwarding
settings to forward incoming service requests to the server(s) on your local network
page 88).
• Use the Port Trigger screen to change your Zyxel Device's trigger port settings
91).
• Use the ALG screen to enable or disable SIP (VoIP) ALG (Application Layer Gateway) in the Zyxel
Device (Section 10.5 on page
C
(Section 10.2 on page
92).
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H A P T E R
88).
(Section 10.4 on page
10

NAT

(Section 10.3 on