Network Address Translation; Overview - ZyXEL Communications NBG-416N User Manual

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Network Address Translation

10.1 Overview

This chapter discusses how to configure NAT on the NBG-416N.
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.
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-
416N 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
A: 192.168.1.33
FTP, Telnet, SNMP
Ports 21 to 25
B: 192.168.1.34
Port 80
C: 192.168.1.35
For more information on IP address translation, refer to RFC 1631, The IP Network
Address Translator (NAT).
NBG-416N User's Guide
LAN WAN
192.168.1.1
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IP address
assigned by ISP
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