A cable modem only assigns one IP address, unless you purchase multiple ones through your Cable ISP.
In order to share one IP with multiple PC's, you cannot rely on a hub unless it has built-in DHCP (which many don't). Without a unique IP, the cable don't know where the incoming traffic should go.
However, I am not saying sharing cable modem via hub is impossible. In fact there is one way to do this.
This way only works when these conditions are met:
1) one of the computers have to have Windows NT installed (Windows 9x can't assign multiple IPs on one NIC). You need multiple IPs to configure 2 TCP/IP subnets on the one NIC - one subnet for LAN and second for link to the modem.
2) the cable modem must have flittering capabilities. It means that modem must filter all packets with local IP addresses - in another words it must be able to send to the Internet (to the ISP) right packets only.
Basically one of the machines will act as a gateway to route all the traffics to the proper computers that are on the subnet
To see how to assign local ip
Here is detail explanations:
http://www.dispi.com/proxyplus/faq/articles/EN/art04103.htm
I don't think the aforementioned method would work if the gateway computer is turned off. Another disadvantage of using a hub is that every PC sharing the bandwidth equally, even when it's not in use.
So the better way to share internet is using a router.
A router usually has NAT (Network Address Translation) technology which uses DHCP and assigns a unique IP address to each networked PC. It also manages the single IP with the cable modem. Plus the network is switched which conserves bandwidth and is ultimately faster.
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