Network Address Translation (Nat); Overview - ZyXEL Communications NBG-417N - V1.0 Manual

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H A P T E R
Network Address Translation

11.1 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 NBG-
417N. 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 NBG-417N, which is 192.168.1.1.
Figure 65 NAT Example
A: 192.168.1.33
FTP, Telnet, SNMP
Ports 21 to 25
B: 192.168.1.34
Port 80
C: 192.168.1.35
This chapter discusses how to configure NAT on the NBG-417N.
NBG-417N User's Guide
LAN WAN
192.168.1.1
NBG-417N
11
(NAT)
IP address
assigned by ISP
117