ZyXEL Communications P-334WT Support Notes page 63

address 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 P-334WT router). The P-334WT 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 P-334WT maps one ILA to one IGA.