ZyXEL Communications P-660 User Manual

P-660 Series Support Notes

we call this feature as 'Multi-NAT'. For more information on IP 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-660 router). The P-660
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:

One to One

In One-to-One mode, the P-660 maps one ILA to one IGA.

Many to One

In Many-to-One mode, the P-660 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).

Many to Many Overload

In Many-to-Many Overload mode, the P-660 maps the multiple ILA to shared IGA.