Re: pcmcia ethernet cards

[Larry Clapp <larry@theclapp.org>]

On Thu, Dec 02, 1999 at 08:36:55AM -0800, Richard Weil wrote:
> I'm planning the following setup:
> 
> - Dell Inspiron 7000, running Debian w/ firewall options
> compiled into the kernel as the "permanently" connected
> machine.
> 
> - On occassion, a second laptop will be networked with the
> Dell, so it can also use the DSL connection [it runs Windows
> 95].
> 
> - Rarely I'll need to bring the Dell with me places and I'll
> want to use a modem.
> 
> With this in mind I think I may need 3 cards (please correct me
> if I'm wrong -- I have never setup a network before). One card
> for the DSL-Dell connection, 2 cards for the PC-PC connection
> [one each]. And I guess one of the three card should be an
> ethernet + modem. Obviously, this means 2 cards in the Dell.
> 
> Any advice would be greatly appreciated.

Just by the way, you don't *have* to have three cards.  I have a
setup vaguely similar to the one you've described, at least as
far as how the network looks:

                           desktop machine (IP addr from DHCP)
    cable modem --- hub --<
                           laptop machine (IP 192.168.39.1)

I use the desktop machine as the router with only one ethernet
card.  The routing tables may look a bit odd, but it does work,
and the collisions on the network are not as high as you might
think -- you can use both machines talking to the net and to each
other, all at the same time.  I got the hub from (I think)
CompUSA for ~$40.

Tracing an outbound packet from the laptop:

    laptop => hub => desktop => hub => cable modem

Inbound packets follow the reverse path.    

The desktop machine does IP Masquerading of the laptop packets,
which is how they get out to the cable modem, and then onto the
Internet.

The big disadvantage to this setup is that, since the desktop
machine gets its IP address from dhcp, occasionally it changes.
(I leave it on all the time, though, so that doesn't happen very
often.)  When that happens, you have to change your routing
tables and your /etc/hosts file.  I do it by hand, but perhaps
one day I'll automate it.  It only happens once every few months,
so it hasn't annoyed me enough, yet.  :)

By comparison, the "normal" set up would look something more like
this:

    cable modem --- desktop machine --- laptop

or possibly

                                             +- laptop
    cable modem --- desktop machine --- hub -+
                                             +- laptop
					     ...

These both require two ethernet cards in the desktop machine, but
then the rest of the network is immune to the desktop's IP
address changing.

-- Larry Clapp

-- 
Larry Clapp / hm: larry@theclapp.org
Great Southern Oxymorons: Grits connoisseur