User’s Guide 125
CHAPTER 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
WANLAN
assigned by ISP
FTP, Telnet, SNMP
Port 80
Ports 21 to 25