ZyXEL Communications 2602RL-D3A manual Using NAT / Multi-NAT, ∙ What is Multi-NAT?

Prestige 2602RL-D3A Support Notes

Using NAT / 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 Prestige, thus preventing intruders from probing your network.

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, 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 Prestige router). The Prestige keeps track of the original addresses and port numbers so incoming reply packets can have their original values restored.

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