How Nat Works; Figure 39 How Nat Works - ZyXEL Communications P-660RU-Tx User Manual

10.6.3 How NAT Works

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

LAN
192.168.1.12
192.168.1.11
P-660RU-Tx User's Guide
192.168.1.13
SA
192.168.1.10
Inside Local
Address
192.168.1.10
Chapter 10 Network Address Translation (NAT)
NAT Table
Inside Local Inside Public
IP Address
IP Address
192.168.1.10
1
192.168.1.11
2
192.168.1.12
3
192.168.1.13
4
SA
1
Inside Public
Address
WAN
99