ZyXEL Communications ZyXEL Prestige 202, User Manual

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Prestige 202 ISDN Router
NAT
7-1
Chapter 7
NAT (Network Address Translation)
This chapter discusses how to configure NAT on the Prestige.
7.1 Introduction
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 as 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 (for Many-to-One and Many-to-Many Overload
mapping – see ahead), NAT offers the additional benefit of firewall protection. If no server is
defined in these cases, all incoming inquiries will be filtered out by your Prestige, thus preventing
intruders from probing your network. For more information on IP address translation, refer to RFC-
1631,
The IP Network Address Translator (NAT).
7.1.1 Advantages of NAT
l
NAT is a cost-effective solution to access the Internet or other remote TCP/IP networks as
NAT conserves on the number of global IP addresses that a company needs in its
communication with the outside world.
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NAT supports popular Internet applications such as MS Traceroute, CuSeeMe, IRC,
RealAudio, VDOLive, Quake and PPTP with no extra configuration needed.
l
NAT supports servers, including multiple servers of the same type to be accessible to the
outside world.