Connecting an extra computer to Internet

Mikkel L. Ellertson mikkel at infinity-ltd.com
Thu Jul 5 22:30:34 UTC 2007


Ian Malone wrote:
> 
> Do you know what make & model the modem is, and
> have you checked the documentation and manufacturer's
> site?  From another post where you say it's managed
> through a web interface I think it could be a router
> without a switch (they do exist), but it's not
> possible to confirm this without a model number.
> 
> If the web interface mentions DHCP I'd say the odds
> go up significantly.  Also if you can find out what
> gateway your computer is using for its net connection
> a private subnet would probably indicate a router.[1]
> 
It is not unusual for the "modem" to have a web interface. The thing
to keep in mind is that what they are calling a modem for DSL or
cable is not the same as the modem you would use on a voice phone
line. (POTS) Besides modulation and demodulation, it also performs
some of the functions of a router. But the router functions tend to
be limited. It may function as a bridge, or it may do limited NAT.
You may have the option of having the modem make a PPPoE connection
to your ISP, or the modem may just provide the Ethernet connection
that your computer (or firewall/router) makes the PPPoE connection
over. with a web interface, the method used is probably configurable.

One problem people run into with these devices is that they will
only give out one DHCP lease at a time. You usually end up either
power-cycling the modem if you want to change computers, or cloning
the MAC address of the computer you used to configure it. This is
why most home firewall/routers have an option to clone the mac
address you are using to configure the router, and/or set a specific
MAC address. (Things are different if you are paying for more then
one IP address, but that is not the normal home setup.) This is why
you can not just add a hub or switch and connect up more then one
computer. there are ways to make it work, by setting up the first
computer to do NAT or Internet connection sharing.

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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