Archived from groups: alt.comp.hardware.pc-homebuilt (
More info?)
Scott wrote:
> Hi all,
>
> I was wanting to connect my cable modem to my pc and xbox but do not want
> the have to have the pc on to do this.
>
> I've been told to get a router, but i was wondering, what is the difference
> between a router and an Ethernet hub?
>
> I purchased a network starter kit years ago and have just recently found the
> hub again.
>
> Can this do the same job? What are the differences?
>
> Many thanks for any help given,
>
> Scott
>
>
The key to this is what kind of cable modem you have. If you have one that
is designed to operate with multiple computers then it will have the router
function built in: I.E. NAT (Network Address Translation) and a DHCP server
to dole out IP addresses to the computers on the local LAN (and probably a
firewall). In which case you could simply add a hub: a dumb device that is
essentially an wire interconnect box.
If, however, you have a simple 'one computer' cable modem (more likely I
would think in your case) then you'll need to add a router that has NAT and
a DHCP server to dole out IP addresses to the computers on the local LAN.
Now, when you use the 'one' computer connected to the cable modem as the
'internet connection sharing' box, that is what it's doing: acting as a NAT
router (the 'internet connection sharing' part) and a DHCP server for the
other computers. It is, 'the router'. Or, as you want to do, you can buy a
stand alone one to do the same job.
Here's how it works.
You can't use internet addresses for your local LAN and local LAN IP
addresses are not valid on the internet so you need something 'in-between'
and some means to 'translate' between the two. For a single computer there
is really nothing to figure out, though; the cable modem knows where
everything comes from and goes to: the one computer. So it is essentially a
one to one echo between them.
With more than one computer it becomes more problematic. Each could make a
request to the modem but when the answer comes back, where does it go?
Something must keep track of those requests and match the replies up with
them so they go back to the requesting computer. In other words, something
must route the data. That's what NAT does: keep track of who asked and then
route the reply to them.
Now, each machine needs a local LAN IP address so NAT knows who's talking.
One could do that manually but it's a lot nicer if the router handles it
automatically so NAT routers usually include a DHCP server. And, since
we've got a microprocessor in the thing already to do NAT and DHCP, we
might as well add a firewall feature, right?
Note that it isn't just 'a router' you need. You need a NAT router.
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