Setting up a network and sharing internet

[Henry Spencer]

On Thu, 18 Aug 2005, Steve wrote:
> Is there a way where I would not require a crossover cable?

An Ethernet port transmits on one pair of wires and receives on another,
and to connect two together, there *must* be a crossover somewhere, so
that each port's transmitter pair is connected to the other's receiver. 

Ethernet hubs (switches, etc.) have built-in crossovers, so you use
straight cables to connect hosts to hubs.  You can avoid needing a
crossover cable by buying a hub instead, and using two straight cables to
connect the two hosts to the hub.  If you're going to have more than two
machines eventually, that's what you should do, because a crossover cable
works only for exactly two machines -- there is no cable-only method for
larger numbers.  However, if you're only concerned about two, a crossover
cable will be cheaper than a hub plus two straight cables. 

As I noted earlier, *some* Ethernet ports have built-in crossovers which
they can turn on and off, and are smart enough to adapt themselves to
whatever's on the other end.  This is starting to be common in hubs, but
is not yet widespread in hosts. 

(Terminology:  a "switch" is just a smart hub.  Most hubs you can buy now
are in fact switches; for your purposes the difference is unimportant.)

> Can I make my
> Linux machine a router, and would that mean I could use a normal ethernet
> cable out of the NIC port to run into the laptop?

No.  Making your Linux machine a router just affects how it handles
incoming packets; that's a higher-level issue, done in software.  Making
it talk to the laptop at all still requires a crossover somewhere; that's
a hardware requirement, not something software can change. 

(Boxes built as routers, like hubs, will often have built-in crossovers
in their hardware, so hosts can connect to them with straight cables.)

                                                          Henry Spencer
                                                       henry-lqW1N6Cllo0sV2N9l4h3zg at public.gmane.org

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