ZyXEL Communications Prestige 2302RL Support Notes page 21

The SUA feature that the Prestige supports previously operates by mapping the private IP addresses to a global
IP address. It is only one subset of the NAT. The Prestige with ZyNOS V3.40 supports the most of the features
of the NAT based on RFC 1631, and we call this feature as 'Multi-NAT'. For more information on IP address
translation, please refer to RFC 1631,

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 Prestige router). The Prestige keeps track of the original addresses and port numbers so incoming
reply packets can have their original values restored.
1. NAT Mapping Types
NAT supports five types of IP/port mapping. They are:
2. One to One
In One-to-One mode, the Prestige maps one ILA to one IGA.
3. Many to One
In Many-to-One mode, the Prestige 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).
The IP Network Address Translator (NAT)
All contents copyright (c) 2007 ZyXEL Communications Corporation.
Prestige 2302RL Support Notes
.
21