ZyXEL Communications NBG410W3G Series - Manual (Page 33)

NBG410W3G Support Note
All contents copyright (c) 2008 ZyXEL Communications Corporation.
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translation, please refer to RFC 1631, The IP Network Address Translator (NAT) .
• 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 NBG410W3G router). The NBG410W3G 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 NBG410W3G maps one ILA to one IGA.
2. Many to One
In Many-to-One mode, the NBG410W3G 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