ZyXEL Communications Corporation NBG416N Manuel D’Utilisation
NBG-416N User’s Guide
101
C
H A P T E R
11
Network Address Translation
(NAT)
11.1 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.
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.
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 59 NAT Example
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