Internet Connection Sharing Configuration

Q.  Why can't I just connect a cable MODEM directly into my Ethernet hub and configure my five computers to talk it via the hub?

A.  You can if you want to pay for additional Internet Protocol (IP) addresses.  Most ISPs charge a monthly fee for additional IP addresses.  Each computer connected directly (via the network NIC MODEM) to the Internet has to have a unique IP address.  Your cable company/Internet Service Provider (ISP) "own" the ones that can connect to the Internet via the ISP's network.  You only need one ISP-provided IP from the cable company if you use Internet Connection Software (ICS), such as SyGate and the ICS software which comes with Windows Me and Windows 98 Second Edition.  Each computer will have a unique IP assigned locally by ICS (the cable company doesn't see these local IPs; it "thinks" it is dealing with one network node/computer: the NAT--Network Address Translator). The NAT interfaces the local IPs to the single IP assigned by the cable company's Dynamic Host Configuration Protocol (DHCP) server to the cable MODEM (this discussion also applies to DSL and ISDN connections). The NAT translates packets (IP headers) sent back and forth between the two networks. You DO need two NICs in the computer which is connected to the cable MODEM because you will be interfacing with two networks which cannot talk to each other through the same NIC. Picture ICS as a software gateway which can talk to, and translate between both networks.

Update: The latest version of SyGAte is advertised to work with one network adapter.  Also, hardware Internet routers, such as the SMC Barricade, only require one network adapter in each computer.