Cable or docis modems work differently then DSL does. Docsis modems put out a normal ethernet connection on their ethernet interface. DSL modems on the other hand use whats called PPoE or Point to Point over Ethernet, simliar to the old dialup that windows 3.11 and win95 used with Trumpet_winsock [I'm dating myself here] and the dialup software that win98 on up has as standard, that requires client software.
All these issues are solved with the addtion of a gateway router/firewall. The gateway router firewalls get a DHCP address from the provider, whether cable or telco. Once the gateway/router has it they use a service called NAT or Network Address Translation. The inside of the firewall [your house] normally gets whats called a non-routable IP address in the 192.168.x.x range or you can change it to a non-routable class 'A' address of 10.x.x.x, at least the SMC ones will handle the 10 address space, not sure about the other brands. They then translate any outgoing requests from your inside network and make it appear the requests are coming from the single IP that is on the outside of the router/gateway.
Cable companies don't like router/firewalls because they can't see how many machines you have and it offends their sense of greed because they think you are getting away with something for free. DSL on the other hand is from the telcos who are used to working with real networks where you pay for bandwidth not machines, I was on my local cableco $hit list for a long time because I was installing SMC's on every one of my customers cable setups and they did not like it plus I was selling moto surfboards faster than they could replace their failed scientific altantas :laugh3:
I have between 5 and 10 systems here at any one time, sometimes more when doing a big build and I for sure use bandwidth when doing updates on 20 or 30 new machines all at once.
Oh well, back to burning ISO's...