ZyXEL Communications 2WG - Manual (Page 27)

ZyWALL 2WG Support Notes
All contents copyright (c) 2006 ZyXEL Communications Corporation.
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• How NAT works
If we define the local IP addresses as the Internal Local Addresses (ILA) and the global IP addresses as the
Inside Global Address (IGA), see the following figure. The term 'inside' refers to the set of networks that are
subject to translation. NAT operates by mapping the ILA to the IGA required for communication with hosts on
other networks. It replaces the original IP source address (and TCP or UDP source port numbers) and then
forwards each packet to the Internet ISP, thus making them appear as if they had come from the NAT system
itself (e.g., the ZyWALL router). The ZyWALL keeps track of the original addresses and port numbers so
incoming reply packets can have their original values restored.
• NAT Mapping Types
NAT supports five types of IP/port mapping. They are:
1. One to One
In One-to-One mode, the ZyWALL maps one ILA to one IGA.
2. Many to One
In Many-to-One mode, the ZyWALL maps multiple ILA to one IGA. This is equivalent to SUA (i.e., PAT,
port address translation), ZyXEL's Single User Account feature that previous ZyNOS routers supported
(the SUA only option in today's routers).
3. Many to Many Overload
In Many-to-Many Overload mode, the ZyWALL maps the multiple ILA to shared IGA.
4. Many One to One
In Many One to One, the ZyWALL maps each ILA to unique IGA.