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

A: 192.168.1.33

LAN

 

WAN

FTP, Telnet, SNMP

 

 

Ports 21 to 25

 

 

 

 

 

 

 

 

 

 

192.168.1.1

B: 192.168.1.34

Port 80

IP address assigned by ISP

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.

20.1.1What 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).

 

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NBG4615 User’s Guide