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Laptop-to-laptop Ethernet connection

Sometimes I take train with my spouse. I have a Linux laptop and a
Sierra 597E "wireless broadband" card. This card works great with
Linux, its maker Sierra contributes to the Linux kernel, and I
basically have a well working internet while on train.

The question concerns the second laptop -- my wife's. 

What I would like is to connect it to my laptop via Ethernet, and have
her laptop use my laptop as a "gateway". 

My question is, can I directly connect them. I think that some pairs
in Ethernet cable are somehow twisted, making a direct connection from
computer to computer unusual, usually they are connected through a hub
or some such. 

Would two computers see each other if they are directly connected?

Then the last thing that I need, I think, is to set up and configure
dhcpd in a certain way. 

i
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Ignoramus10962
2/15/2008 8:47:10 PM
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On Fri, 15 Feb 2008 14:47:10 -0600, Ignoramus10962 wrote:

> My question is, can I directly connect them.

Yes, but you need a crossover cable.

0
daveuhring (1186)
2/15/2008 8:53:16 PM
On 2008-02-15, Dave Uhring <daveuhring@yahoo.com> wrote:
> On Fri, 15 Feb 2008 14:47:10 -0600, Ignoramus10962 wrote:
>
>> My question is, can I directly connect them.
>
> Yes, but you need a crossover cable.
>

Yes, that's the thing, thanks. I will try to make one tonight (I have
a crimper)

i
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Ignoramus10962
2/15/2008 9:05:16 PM
On 2008-02-15, Dave Uhring <daveuhring@yahoo.com> wrote:

>> My question is, can I directly connect them.
>
> Yes, but you need a crossover cable.

Not unless the laptops are both pretty old.  AFAICT, everything
made in the last 5-7 years uses auto-sensing PHYs that will
flip tx/rx pairs as needed.  Plug in a straight-through patch
cable and it'll probably work (only one of the laptops needs to
auto-sense).

-- 
Grant Edwards                   grante             Yow! Were these parsnips
                                  at               CORRECTLY MARINATED in
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grante (5416)
2/15/2008 9:07:35 PM
Dave Uhring wrote:
> On Fri, 15 Feb 2008 14:47:10 -0600, Ignoramus10962 wrote:
> 
>> My question is, can I directly connect them.
> 
> Yes, but you need a crossover cable.
> 
Not necessarily. Modern NICs seem to detect if you need a crossover cable
and fix it themselves. Here is one.

http://www.intel.com/network/connectivity/products/pro1000pt_desktop_adapter.htm

-- 
  .~.  Jean-David Beyer          Registered Linux User 85642.
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 ^^-^^ 16:15:01 up 2 days, 22:26, 0 users, load average: 4.10, 4.16, 4.10
0
jeandavid8 (983)
2/15/2008 9:33:24 PM
I demand that Dave Uhring may or may not have written...

> On Fri, 15 Feb 2008 14:47:10 -0600, Ignoramus10962 wrote:
>> My question is, can I directly connect them.

> Yes, but you need a crossover cable.

But check a straight-through cable anyway - you'll probably find that one (or
both) of the ports will detect this and adjust accordingly.

-- 
| Darren Salt    | linux or ds at              | nr. Ashington, | Toon
| RISC OS, Linux | youmustbejoking,demon,co,uk | Northumberland | Army
| + Generate power using sun, wind, water, nuclear.      FORGET COAL AND OIL.

The Ranger isn't gonna like it, Yogi.
0
news64 (1253)
2/15/2008 9:46:08 PM
> What I would like is to connect it to my laptop via Ethernet, and have
> her laptop use my laptop as a "gateway". 
> 
> My question is, can I directly connect them. I think that some pairs
> in Ethernet cable are somehow twisted, making a direct connection from
> computer to computer unusual, usually they are connected through a hub
> or some such. 

To be safe, you need a cross over cable.  You could gamble a straight
cable and auto sensing, but a cross over cable will/should work.  You
don't really need dhcpd to make the connection.  You can hard code IPs and
routes and be fine.  You will need NAT / iptables on the gateway to do the
bridging.  Although there's probably other ways to make it work.  You
might also need dns caching unless you manually edit the clients
resolv.conf or make dhcpd handle the propagation.  It's certainly doable. 
One way or another.
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wwwShadow7 (310)
2/15/2008 10:01:06 PM
On Fri, 15 Feb 2008 21:46:08 +0000, Darren Salt wrote:

> I demand that Dave Uhring may or may not have written...
> 
>> On Fri, 15 Feb 2008 14:47:10 -0600, Ignoramus10962 wrote:
>>> My question is, can I directly connect them.
> 
>> Yes, but you need a crossover cable.
> 
> But check a straight-through cable anyway - you'll probably find that one (or
> both) of the ports will detect this and adjust accordingly.

Now that you mention it, my switch can autoconfigure any of its ports to
be either straight through or cascade.  No reason a NIC couldn't do that.

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daveuhring (1186)
2/15/2008 10:32:11 PM
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