ZyXEL Communications nbg-418n User Manual
NBG-418N User’s Guide
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Network Address Translation
10.1 Overview
This chapter discusses how to configure NAT on the NBG-418N.
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.
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.
Each packet has two addresses – a source address and a destination address. For outgoing packets,
NAT maps private (local) IP addresses to globally unique ones required for communication with
hosts on other networks. It replaces the original IP source address in each packet and then
forwards it to the Internet. The NBG-418N keeps track of the original addresses and port numbers
so incoming reply packets can have their original values restored. The following figure illustrates
this.
NAT maps private (local) IP addresses to globally unique ones required for communication with
hosts on other networks. It replaces the original IP source address in each packet and then
forwards it to the Internet. The NBG-418N keeps track of the original addresses and port numbers
so incoming reply packets can have their original values restored. The following figure illustrates
this.
Figure 72
NAT Example
For more information on IP address translation, refer to RFC 1631, The IP Network Address
Translator (NAT).
Translator (NAT).
Note: You must create a firewall rule in addition to setting up NAT, to allow traffic from
the WAN to be forwarded through the NBG-418N.
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