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VSG-1200 User’s Guide
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Chapter 5 NAT Pool
5.1.2 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, NAT offers the additional benefit of firewall protection. With no servers defined,
your VSG 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)
.
5.1.3 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 in each packet and then
forwards it to the Internet. The VSG keeps track of the original addresses and port numbers so
incoming reply packets can have their original values restored.
5.2 VPN and NAT
A VPN (Virtual Private Network) provides secure communications between sites without the
expense of leased site-to-site lines. A secure VPN is a combination of tunneling, encryption,
authentication, access control and auditing technologies/services used to transport traffic over
the Internet or any insecure network that uses the TCP/IP protocol suite for communication.
The VSG allows subscribers to create a VPN tunnel to a remote site.
By default, the VSG performs NAT on the LAN; mapping multiple private LAN addresses to
a single public address on the WAN. This prevents subscribers from creating multiple VPN
connections to a remote VPN device that allows only one VPN connection per source IP
address.
Note:
For IPSec, the VSG does not support AH protocol.
Summary of Contents for VSG-1200
Page 1: ...VSG 1200 Vantage Service Gateway User s Guide Version 1 08 1 2006 ...
Page 8: ...VSG 1200 User s Guide 8 Customer Support ...
Page 22: ...VSG 1200 User s Guide 22 List of Figures ...
Page 26: ...VSG 1200 User s Guide 26 List of Tables ...
Page 40: ...VSG 1200 User s Guide 40 Chapter 2 Hardware Installation and Connection ...
Page 45: ...VSG 1200 User s Guide Chapter 3 The Web Configurator 45 Figure 13 System Setting System ...
Page 52: ...VSG 1200 User s Guide 52 Chapter 3 The Web Configurator ...
Page 64: ...VSG 1200 User s Guide 64 Chapter 4 LAN WAN and Server Setup ...
Page 74: ...VSG 1200 User s Guide 74 Chapter 6 Authentication Figure 29 System Setting Authentication ...
Page 102: ...VSG 1200 User s Guide 102 Chapter 9 Dynamic Subscriber Accounts ...
Page 128: ...VSG 1200 User s Guide 128 Chapter 13 Subscriber Information Window ...
Page 136: ...VSG 1200 User s Guide 136 Chapter 14 Account Printout ...
Page 140: ...VSG 1200 User s Guide 140 Chapter 15 User Agreement Page ...
Page 144: ...VSG 1200 User s Guide 144 Chapter 16 Bandwidth Management ...
Page 158: ...VSG 1200 User s Guide 158 Chapter 19 LAN Devices ...
Page 162: ...VSG 1200 User s Guide 162 Chapter 20 Static Route ...
Page 170: ...VSG 1200 User s Guide 170 Chapter 21 Syslog and Session Trace ...
Page 174: ...VSG 1200 User s Guide 174 Chapter 22 SNMP ...
Page 198: ...VSG 1200 User s Guide 198 Chapter 25 Secure Socket Layer ...
Page 206: ...VSG 1200 User s Guide 206 Chapter 26 The SMT ...
Page 214: ...VSG 1200 User s Guide 214 Chapter 27 LAN and WAN Setup Using the SMT ...
Page 226: ...VSG 1200 User s Guide 226 Chapter 28 Configuration and Firmware Maintenance ...
Page 236: ...VSG 1200 User s Guide 236 Appendix B IP Address Assignment Conflicts ...
Page 238: ...VSG 1200 User s Guide 238 Appendix C Subscriber Login ...
Page 242: ...VSG 1200 User s Guide 242 Appendix D Vendor Specific Attributes ...
Page 252: ...VSG 1200 User s Guide 252 Appendix F Cable Types and Cable Pin Assignments ...
Page 264: ...VSG 1200 User s Guide 264 Appendix G Setting up Your Computer s IP Address ...
Page 272: ...VSG 1200 User s Guide 272 Appendix H IP Subnetting ...