ZyXEL Communications NBG-417N, User Manual, Page: 124 / 279

User
’
s Guide
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H A P T E R
11
NAT
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
NBG4115. 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 NBG4115, which is 192.168.1.1.
Figure 65 NAT Example
This chapter discusses how to configure NAT on the NBG4115.
Note: You must create a firewall rule in addition to setting up NAT, to allow traffic from
the WAN to be forwarded through the NBG4115.
A: 192.168.1.33
B: 192.168.1.34
C: 192.168.1.35
IP address
192.168.1.1
WAN LAN
assigned by ISP
FTP, Telnet, SNMP
Port 80
Ports 21 to 25
C
om
pan
y
C
on
fiden
tial