User`s manual

P-660 Series Support Notes

5. Using Multi-NAT

What is Multi-NAT?

NAT (Network Address Translation-NAT RFC 1631) is the translation of an Internet

Protocol address used within one network to a different IP address known within

another network. One network is designated the inside network and the other is the

outside. Typically, a company maps its local inside network addresses to one or more

global outside IP addresses and "unmaps" the global IP addresses on incoming

packets back into local IP addresses. The IP addresses for the NAT can be either fixed

or dynamically assigned by the ISP. In addition, you can designate servers, e.g., a web

server and a telnet server, on your local network and make them accessible to the

outside world. If you do not define any servers, NAT offers the additional benefit of

firewall protection. In such case, all incoming connections to your network will be

filtered out by the P-660, thus preventing intruders from probing your network.

The SUA feature that the P-660 supports previously operates by mapping the private

IP addresses to a global IP address. It is only one subset of the NAT. The P-660 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, 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