From:           	Michael Price <[log in to unmask]>

> To connect them directly you need a twisted pairs ethernet cable. Most
> PC outlets would have one.

  All modern Ethernet cables are "twisted pair" -- the 8 wires 
are grouped in pairs, each of which is twidted together to 
reduce interference.

  The cable that he needs is a *crossover*, which changes the 
mapping of which pair goes to which pins, a separate 
characteristic from whether each pair is twited inside the 
cable.

  [Simple test:  Each of the eight wires is color-coded.  In a 
normal Ethernet cable, if you hold up the clear plastic 
connectors beside each other, you'll see the same colour 
sequence at each end.  If the cable is a crossover, the "send" 
at oneend connects to the "receive" at the other, and vice 
versa, and so the colour sequencs will be different.]

  The normal state of affairs is for an Ethernet cable to 
connect a computer to a hub or switch -- whose ports are wired 
the other way from a computer.  Yes, if we had a time machine, 
we could go back about 20 years and decree that all ethernet 
ports would be wired the same and all ethernet cables would be 
crossovers, but it's too late now.

  In our world, crossovers exist to connect switches to other 
switches and computers to other computers.

  Using the right cable takes care of the physical connection 
(you'll stop getting that "A cable is unplugged" message).  And 
devices should get layer 2 right almost by definition.  But at 
layer 3 they will each need an IP address and a suitable mask -- 
and those need to fall within the same "subnet" without 
colliding with anything else.

  IF you will be using ICS (Internet Connection Sharing), 
Windows will take care of this for you, if rather hamfistedly.  
If not, you are going to have to do it manually.  Use the common 
mask value 255.255.255.0 and pick one of the bocks of reserved 
*private* addresses 192.168.x.y, where x is a number between 0 
and 255 (0 and 1 are popular choices by makers of home routers, 
so I use 144), and y are two numbers -- one for each PC -- 
between 1 and 254 (0 and 255 are reserved for other uses).
  You can test the connection using the "ping" command line 
command.  For instance, from PC 192.168.144.1, you run "ping 
192.168.144.2" and should see that the other machine is 
answering.

  Ideally, you should be able to refer to the machines by name 
rather than by address, but check with the address first so you 
know if you are seeing a connection poblem or a name-resolution 
problem.  (Behind the scenes, each name must be "resolved" to an 
address.)

David Gillett

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