P-660R-T Series User’s Guide
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Chapter 7 Network Address Translation (NAT) Screens
7.1.2 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, for example, 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
NAT offers the additional benefit of firewall protection. With no servers defined, your
Prestige 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)
.
7.1.3 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 Prestige keeps track of the original addresses and port
numbers so incoming reply packets can have their original values restored. The following
figure illustrates this.
Summary of Contents for ADSL2+ 4-port Gateway P-660H-D Series
Page 1: ...P 660R T Series ADSL2 Ethernet Gateway User s Guide Version 3 40 6 2005 ...
Page 23: ...P 660R T Series User s Guide 23 ...
Page 27: ...P 660R T Series User s Guide 27 ...
Page 31: ...P 660R T Series User s Guide 31 Introduction to DSL ...
Page 39: ...P 660R T Series User s Guide 39 Chapter 1 Getting To Know Your Prestige ...
Page 57: ...P 660R T Series User s Guide 57 Chapter 4 Password Setup ...
Page 65: ...P 660R T Series User s Guide 65 Chapter 5 LAN Setup ...
Page 75: ...P 660R T Series User s Guide 75 Chapter 6 WAN Setup ...
Page 87: ...P 660R T Series User s Guide 87 Chapter 7 Network Address Translation NAT Screens ...
Page 95: ...P 660R T Series User s Guide 95 Chapter 10 Remote Management Configuration ...
Page 107: ...P 660R T Series User s Guide 107 Chapter 11 Universal Plug and Play UPnP ...
Page 127: ...P 660R T Series User s Guide 127 Chapter 14 Menu 1 General Setup ...
Page 131: ...P 660R T Series User s Guide 131 Chapter 15 Menu 2 WAN Backup Setup ...
Page 135: ...P 660R T Series User s Guide 135 Chapter 16 Menu 3 LAN Setup ...
Page 157: ...P 660R T Series User s Guide 157 Chapter 19 Static Route Setup ...
Page 161: ...P 660R T Series User s Guide 161 Chapter 20 Bridging Setup ...
Page 177: ...P 660R T Series User s Guide 177 Chapter 21 Network Address Translation NAT ...
Page 205: ...P 660R T Series User s Guide 205 Chapter 24 System Information and Diagnosis ...
Page 217: ...P 660R T Series User s Guide 217 Chapter 25 Firmware and Configuration File Maintenance ...
Page 223: ...P 660R T Series User s Guide 223 Chapter 26 System Maintenance ...
Page 227: ...P 660R T Series User s Guide 227 Chapter 27 Remote Management ...
Page 237: ...P 660R T Series User s Guide 237 Chapter 28 IP Policy Routing ...
Page 241: ...P 660R T Series User s Guide 241 Chapter 29 Call Scheduling ...
Page 253: ...P 660R T Series User s Guide 253 Chapter 30 Troubleshooting Figure 173 Java Sun ...
Page 257: ...P 660R T Series User s Guide 257 Appendix A ...
Page 281: ...P 660R T Series User s Guide 281 Appendix C IP Subnetting ...
Page 284: ...P 660R T Series User s Guide Appendix D Splitters and Microfilters 284 ...
Page 285: ...P 660R T Series User s Guide 285 Appendix D Splitters and Microfilters ...
Page 287: ...P 660R T Series User s Guide 287 Appendix E Command Interpreter ...
Page 295: ...P 660R T Series User s Guide 295 Virtual Circuit Topology ...