Reference Manual

Internet Connection Sharing Devices

Introduction

ICS devices such as DSL Routers, Cable Modem Routers and 3G Routers are small, stand-alone modules about the size of an Ethernet Switch. They are used to connect a small number of machines on a single private LAN (wired or wireless) to the Internet via a single Internet connection. They work very much like software IP routers such as NAT32 and perform Network Address Translation and TCP/UDP Port Mapping. Some (such as the FritzBox) also have certified firewall functionality and are an ideal replacement for firewall software running on each individual machine. They have the advantage that they are small, low-power devices that can be left switched on and permanently connected to the Internet.

Hardware

ICS devices such as the FritzBox 7390 are powered by a single-chip embedded processsor (MIPS@500 MHz) and contain 128 MB of RAM and 16 MB of flash memory. WiFi (802.11n), Gigabit Ethernet and a 4-port Ethernet switch are also supported. The FritzBox is also fairly unique in that it contains telephony hardware (POTS, ISDN and DECT). It can thus also serve as a home PBX and supports direct VoIP, requiring no VoIP Service Provider.

Software

The software controlling the ICS device is usually stored in Flash memory. Manufacturers of the more expensive devices (such as the FritzBox) provide regular firmware updates, whereas the cheaper devices are often unsupported after a year or two. This can be a problem in the rapidly evolving world of networking. For example, new mobile technologies are appearing all the time, and will continue to do so during the transition from 3G to 4G (LTE).

Limitations

The crucial disadvantage of such devices is that they use the registered IP address entirely for themselves. In other words, none of your machines have full, registered IP address access to the Internet. All your machines have Address Translated access only, meaning that many of the typical "NAT-hostile" applications such as NetMeeting and other H.323-based applications will give trouble.

With NAT32, the machine on which it runs has unmodified access to the Internet, and all applications on that machine will function correctly.

A second problem is that most ICS devices will not allow machines on networks behind a gateway on your private LAN to share the connection at all. This will rarely be a problem for home users, but it may become a problem for small business users, particularly as the business expands.

Finally, most ICS Devices support one network type only. If you start out with a DSL connection and later decide to upgrade to Cable, you may need to purchase a new ICS Device for that purpose.

NAT32 Advantages

The main advantage of NAT32 is its flexibility. It can be configured to support any type of Internet connection available on the host system, and runs on low-cost, low-performance Windows XP systems and higher.

Many powerful features are available, such as support for multiple Internet connections, support for multiple private networks, and customisation via a powerful set of shell commands and Tcl scripts.

Because of its versatility, NAT32 is not a "point and click" application. To configure many of its advanced features, careful study of the Help Pages is essential.