On 1 Feb 99, at 22:45, Changhsu P. Liu wrote:

> I'm trying to network my PC to my Mac to share files and possibly
> sharing the internet connection. I'm not sure how to set up my TCP/IP
> numbers. I have the same TCP/IP numbers on both Machines for internet
> access. On Windows, the number is assigned from Dialup networking so
> that the number is connection specific and not machine specific. To
> connect 2 computers with ethernet, it seems that I need to attach a
> TCP/IP number to the machine from network neighborhood. What number
> should I give for the ethernet network? Do I just give any number as
> TCP/IP, submask, etc... as I like? If I use the same number as my
> internet connection, then is there a conflict with another machine
> which uses the same numbers?

  Each of your machines has an interface to connect to your ISP.  You
have one IP address assigned by your ISP (not all ISPs work this
way...), and it may be used for both of these interfaces AS LONG AS you
only actually USE one at a time.

  To network the computers together, you'll need to add a second
interface to at least one of them.  In your current case, it may be
simplest to add secoind interfaces to both of them.

  These new interfaces will be on a separate network, your internal
LAN.  The addresses and submask you assign on the LAN will determine
which systems your machines see as "local" and which they will try to
dial out to the Internet to reach.
  On a given network, each machine needs a unique address.  The portion
of the address corresponding to the network submask needs to be the
same for all machines on that subnet (which is why it's called a
"subnet mask" ...).  It's also important that no two separate
interfaces have the same IP address on connected networks, so you can't
*quite* go assigning them at random.
  There are special reserved blocks of addresses which can be used for
internal LANs because standard networking equipment won't propagate
them out onto the Internet.  For the smallest LANs, the common address
range is 192.168.xx.yy, with a subnet mask of 255.255.255.0, where xx
must be 0-255 and the same for the whole subnet, and yy must be 1-254
(0 and 255 have reserved meanings) and unique to each machine.  You'll
want each machine to have a "hosts" file listing these addresses, if
you want to refer to the machines by name instead of address.

  If you add an ethernet card to both machines, they can keep their ISP
access, subject as I said to the limitation that they can't both go
online at once.
  Another possibility, though, is to retain external connectivity on
only one machine, and make it the "gateway" for the LAN.  This lets
both machines, and any you later add, share a single ISP connection.
  The drawback is that your gateway machine now "owns" the address
assigned by your ISP.  None of your other machines *has* an external
address any more.  The solution is a technique called Network Address
Translation (NAT), where the gateway machine forwards packets between
the external and internal networks.  I believe you can still download a
free version of WinGate for a two-station network (more costs some
money).  Microsoft recently bought one of their competitors, and so
this will show up as a new feature in the next "Service Pack" for Win98.


David G

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