Connecting an extra computer to Internet

[Kevin J. Cummings]

Paul Smith wrote:
> On 7/5/07, Rick Stevens <rstevens at internap.com> wrote:
>> > > > I have a cable-based (not optic) modem/router to connect to the
>> > > > Internet (ADSL), which works fine. However, a friend comes in from
>> > > > time to time, bringing her laptop. Is there some cheap and easy
>> way of
>> > > > letting her laptop to connect to Internet? Unfortunately, I
>> cannot see
>> > > > any place in the modem/router to connect an extra cable...
>> > >
>> > > Do you have a router installed, or are you connecting your computer
>> > > directly to the DSL modem? The two are usually separate devices, with
>> > > the router sitting between the modem and the computer. Routers
>> > > generally have at least 4 network jacks. The one I use at home is a
>> > > wireless router as well, which is much more convenient for laptops.
>> >
>> > Thanks, Sultan Saini. I am connecting my computer directly to the DLS
>> > modem (provided by my ISP). I think my DLS model is also a router, as
>> > its configuration is done through a web interface.
>>
>> Your modem contains a router.  ADSL needs that.  The question is,
>> how does your computer plug into the modem?  If it uses an RJ45
>> connector (a cable that looks like the cord you use to plug your phone
>> into the wall--but with 8 pins rather than 4), then the easiest way to
>> do it is:
>>
>>     ADSL line <--> existing modem <--> switch <--> computer
>>                                               <--> 2nd computer
>>                                               <--> 3rd computer
>>
>> The "switch" is an item you can buy for $20 US at most stores.  Many
>> companies actually make an ADSL modem/router/switch/WAN access point
>> combo box.
>>
>> For example, D-Link's DSL-2640B is an ADSL modem, router/firewall,
>> 4-port gigabit switch and 802.11g wireless access point.  The URL is
>> http://www.dlink.com/products/?sec=1&pid=567.  Other companies (Airlink,
>> Cisco, etc.) make similar beasties.
>>
>> One of these should be enough for you to do full-up networking at home.
>> If you're unfamiliar with wireless networking, make sure you set the
>> ESSID and WEP key or WPA passphrases to something other than the default
>> so other wireless users can't hijack your bandwidth.  I even go so far
>> as to not have the wireless stuff broadcast the ESSID.  If you don't
>> know my ESSID, you can't find it.  Just because I'm paranoid doesn't
>> mean they aren't out to get me!
> 
> Thanks, Rick and all other respondents. Yes, my DSL modem connects to
> my computer by using an RJ45 connector. The shopkeeper where I went to
> buy a switch claims that the switch may not work and that I should
> instead buy a router. So, I would like to ask you whether it is really
> as he claims.

Well, that depends.  Some DSL/Cable modems will only work if they see
only 1 MAC address on your side of the modem.  Others may require to be
re-booted in order to recognize a new MAC address.  In both cases, the
modem may only talk to only 1 device on your side.  This is where a
router can be more helpful than a switch.  The router can be configured
 to spoof the MAC address of your computer while NATing any other
computers you might set up.  *OR* it will act as a single MAC address
for your internal network, and can be configured to NAT everything you
have inside to the outside world.

>From what *I* have seen of DSL modems, they only want to talk with 1
computer.  You have to have a wireless/router/DSL modem (and it usually
has more than one 1 ethernet port) in order to talk to more than one
computer on your local network side.  My daughter has such a beast from
Verizon in her apartment.  Her roommate can either connect via wireless
connection, or run a long ethernet cable to the router.

The suggestion of adding a 2nd ethernet card to *your* computer will
usually work as well, but you have to set up your own local network for
the 2nd ethernet card, and then be able to set up you computer for IP
forwarding and possibly even NAT.  I know this works, because I used to
do this before I broke down and bought a wireless router for my home
network.

All of this is basic home networking and should be covered my the Home
Network HOWTO that someone else pointed you to.  You have to *know* what
your DSL modem is capable of in order to know what your best solution is.

> Paul

-- 
Kevin J. Cummings
kjchome at rcn.com
cummings at kjchome.homeip.net
cummings at kjc386.framingham.ma.us
Registered Linux User #1232 (http://counter.li.org)