ZyXEL NBG4615 User Manual download pdf (Page 171)

NBG4615 User’s Guide 171

CHAPTER 20

NAT

20.1 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 NBG4615. 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 NBG4615, which is

192.168.1.1.

Figure 108 NAT Example

This chapter discusses how to configure NAT on the NBG4615.

Note: You must create a firewall rule in addition to setting up NAT, to allow traffic from

the WAN to be forwarded through the NBG4615.

20.1.1 What You Can Do

•Use the General screen to enable NAT and set a default server (Section 20.2 on page 173).

•Use the Application screen to change your NBG4615’s port forwarding settings (Section 20.3 on

page 174).

A: 192.168.1.33

B: 192.168.1.34

C: 192.168.1.35

IP address

192.168.1.1

WANLAN

assigned by ISP

FTP, Telnet, SNMP

Port 80

Ports 21 to 25

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ZyXEL NBG4615 User Manual Page 171