Nat; Chapter 20 Nat; Overview; What You Can Do - ZyXEL Communications NBG4615 User Manual

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
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 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
• Use the Application screen to change your NBG4615's port forwarding settings
page 174).
NBG4615 User's Guide
C
HAPTER
LAN WAN
192.168.1.1
IP address
assigned by ISP
(Section 20.2 on page
(Section 20.3 on
2 0

NAT

173).
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