Linux Proxy NIC interfacing woes

[dmartin at ne.arris-i.com (Derek Martin)]

On Fri, 24 Dec 1999, Wass wrote:

> 
> Hello Linux gurus,
> 
> 	I'm running into a problem trying to set up my linux-based
> proxy.  Basically, my NIC cannot see the cable modem, or vice versa.
> Read on for more details.
> 
> 	I've got a cable-modem, which I've successfully used with linux
> for several months now, with a Acer card (compatible with Via-Rhine).
> After getting a new computer, some NIC's, and an 8-port hub, I decided
> to try my hand at setting up a LAN.  

I'm not sure exactly what you mean by "proxy" because it can have a couple
of different (but similar) meanings, but I think you mean you want one
machine to act as a gateway for your network.  If not, the next couple of
paragraphs will be of limited use to you, but should still be at least
somewhat helpful.

If the Acer card is the one that you originally set up your cable modem
for, then that's the only one that will get an IP address from the cable
modem.  The cable company takes the MAC address of the card you set it up
with and only provides DHCP to THAT CARD.  Therefore if you want to make a
different machine a proxy server, you need to put the Acer card in it, and
connect it to the cable modem. Or call the cable company and tell them you
got a new ethernet card, and give them the MAC address for that card.  
Then you need to put a second NIC in it, and assign it a static IP address
on a private address block, such as 192.168.1.1 and stick it in your hub.

Now configure your second machine's card with another static IP address on
that same network, and stick it in the hub.  Configure the default route
on the second machine to point to the first machine, and set up IP
masquerading using ipchains.  See the ipchains howto.

> 
> 	I've gone through the dhcpcd mini-HOWTO to get things started.
> This thing is very out of date!  Are there any plans to add entries for
> Mandrake 6.x to it?  I'd help out with his task, if I can get my box running.

I doubt it -- these documents tend to be as distribution independent as
possible.  But if you feel some info is out of date, I suggest you contact
the author/maintainer who should be mentioned in that document somewhere.

But also, I don't think DHCP is your problem.  I'm still not quite sure
what effect you're trying to achieve, since you never specifically
mentioned how you want to use this "proxy" server.  But it sounds to me
like you don't quite have a handle on what your design needs to look like.

Again, the only card that will get an IP address via DHCP is the one that
is directly connected to your CM, whose MAC address was supplied to your
cable company (either by you or by the technician that did the install).
Any other ethernet card anywhere else in your network will need to be
configured statically, unless you set up your own DHCP server to serve IP
addresses to them.  But where you have so few machines, this is hardly
worth the effort to set up, unless you just want to learn how to do it.

If you do set one up, you want to make sure you're not serving DHCP out to
the network your CM is on... your cable company will probably not like
that too much. Your best bet is to make sure you DON'T install the server
on the machine that's connected to the CM.


> 	It alludes to this possibility in the dhcpcd mini-howto, but
> says that if the card is set to 100baseT, just change that setting.  there
> is no detail/info about how to go about this.

You probably will not need to worry about that.  Unless you have an older
card, or a really crappy one, the card connected to the CM should
auto-sense to 10Mb. I don't have any experience with those Acer cards, so
I can't say how well the auto-negotiate.

> 	I've also played around with various module commands.  Trying
> "insmod 3c90x" I get an error: "3c90x.o: init_module: Device or resource busy"
> Why could this be?  ANd I've seen vague implications that I may also
> need to include the 3c59x module, is this true too?

It probably means that either you have support for that card compiled into
your kernel already, or possibly that you don't have such a card.  As for
loading the extra module, you only need one of them... whichever is the
right one for your card.

> 	Also, ifconfig shows only the 'lo' interface, not eth0.

If the card hasn't been configured (via DHCP or an ifconfig command), it
will only show up if you do
  
  ifconfig -a

Also, if you don't have the right module loaded, it won't show up at all,
even with the -a option.  Another way to know if the driver is loaded is
to check for messages about your card(s) in the output of the dmesg
command right after boot time, or to watch closely for such messages as
the system boots.

Note that I've heard SOME cable companies will let you put the CM on a
hub, and configure several machines via DHCP, but you'll still need to
supply them with the MAC address of ALL the ethernet cards, and this
option usually costs extra $$.  I think a friend told me MediaOne does
this now.  Maybe Niall K. can comment on that.  Niall?


-- 
Derek D. Martin
Senior UNIX Systems/Network Administrator
Arris Interactive
derek.martin at ne.arris-i.com

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