Chapter 12 Network Address Translation (NAT) Screens
P-660RU-T v2 User’s Guide
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NAT never changes the IP address (either local or global) of an outside host.
12.1.2 What NAT Does
In the simplest form, NAT changes the source IP address in a packet received from a
subscriber (the inside local address) to another (the inside global address) before forwarding
the packet to the WAN side. When the response comes back, NAT translates the destination
address (the inside global address) back to the inside local address before forwarding it to the
original inside host. Note that the IP address (either local or global) of an outside host is never
changed.
The global IP addresses for the inside hosts can be either static or dynamically assigned by the
ISP. In addition, you can designate servers (a web server and a telnet server, for example) 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
NAT offers the additional benefit of firewall protection. With no servers defined, your ZyXEL
Device filters out all incoming inquiries, thus preventing intruders from probing your network.
For more information on IP address translation, refer to
RFC 1631
,
The IP Network Address
Translator (NAT)
.
12.1.3 How NAT Works
Each packet has two addresses – a source address and a destination address. For outgoing
packets, the ILA (Inside Local Address) is the source address on the LAN, and the IGA (Inside
Global Address) is the source address on the WAN. For incoming packets, the ILA is the
destination address on the LAN, and the IGA is the destination address on the WAN. NAT
maps private (local) IP addresses to globally unique ones required for communication with
hosts on other networks. It replaces the original IP source address (and TCP or UDP source
port numbers for Many-to-One and Many-to-Many Overload NAT mapping) in each packet
and then forwards it to the Internet. The ZyXEL Device keeps track of the original addresses
and port numbers so incoming reply packets can have their original values restored. The
following figure illustrates this.
Figure 42
How NAT Works
Summary of Contents for P-660RU-T3 V2
Page 2: ......
Page 7: ...Safety Warnings P 660RU T v2 User s Guide 7...
Page 8: ...Safety Warnings P 660RU T v2 User s Guide 8...
Page 10: ...Contents Overview P 660RU T v2 User s Guide 10...
Page 16: ...Table of Contents P 660RU T v2 User s Guide 16...
Page 20: ...List of Figures P 660RU T v2 User s Guide 20...
Page 23: ...23 PART I Introduction Introducing the ZyXEL Device 25 Introducing the Web Configurator 29...
Page 24: ...24...
Page 34: ...Chapter 2 Introducing the Web Configurator P 660RU T v2 User s Guide 34...
Page 35: ...35 PART II Wizard Wizard Setup 37...
Page 36: ...36...
Page 48: ...Chapter 3 Wizard Setup P 660RU T v2 User s Guide 48...
Page 50: ...50...
Page 52: ...Chapter 4 Password Setup P 660RU T v2 User s Guide 52...
Page 68: ...Chapter 6 WAN Setup P 660RU T v2 User s Guide 68...
Page 78: ...Chapter 10 Remote Management Configuration P 660RU T v2 User s Guide 78...
Page 90: ...Chapter 11 Universal Plug and Play UPnP P 660RU T v2 User s Guide 90...
Page 101: ...101 PART IV Maintenance and Troubleshooting Maintenance 103 Troubleshooting 115...
Page 102: ...102...
Page 120: ...120...
Page 124: ...Appendix A Product Specifications P 660RU T v2 User s Guide 124...
Page 156: ...Appendix E Virtual Circuit Topology P 660RU T v2 User s Guide 156...
Page 160: ...Appendix F Legal Information P 660RU T v2 User s Guide 160...