ZyWALL 70 Support Notes
All contents copyright (c) 2005 ZyXEL Communications Corporation.
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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 ZyWALL, thus
preventing intruders from probing your network.
The SUA feature that the ZyWALL supports previously operates by mapping the private IP addresses to a
global IP address. It is only one subset of the NAT. The ZyWALL 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 ZyWALL router). The ZyWALL 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:
