ZyXEL Communications P-660RU-Tx Benutzerhandbuch

 Chapter 10 Network Address Translation (NAT)

P-660RU-Tx User’s Guide

Each packet has two addresses – a source address and a destination address. For 
outgoing packets, the inside local address is the source address on the LAN, and 
the inside public address is the source address on the WAN. For incoming packets, 
the inside local address is the destination address on the LAN, and the inside 
public address is the destination address on the WAN. 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 (and TCP or UDP source port 
numbers for Many-to-One and Many-to-Many Overload NAT mapping) in each 
packet and then forwards it to the Internet. The P-660RU-Tx 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 39   How NAT Works

192.168.1.13

192.168.1.10

192.168.1.11

192.168.1.12

SA

192.168.1.10

SA

1

Inside Local
IP Address

192.168.1.10
192.168.1.11
192.168.1.12
192.168.1.13

Inside Public 
IP Address
1
2
3
4

NAT Table

Inside Local

Address 

Inside Public

Address