network problem: internet sharing

[Alma J Wetzker]

>>> Re: network problem: internet sharing
>>> Keith Antoine <kantoine at optusnet.com.au>
>>> Tue, 22 Jul 2003 18:58:48 -0400
>>>
>>>
>>>On Tuesday 22 July 2003 12:25 am, Alma J Wetzker wrote:
>>>>Keith,
>>>>
>>>>The modem goes to the linux box through an ethernet card.  The linux box
>>>>works.  The linux box has a second ethernet card that is connected to
>>>>the XP box elsewhere.  The XP box can ping the linux box.  (I hope this
>>>>is correct.)
>>>
>>>yes
>>>
>>>>Can the XP box ping an address on the wild wild web?  (Using the ip
>>>>address as the name will not work.)  If it can then the issue could be
>>>>the linux box not routing the DNS lookup correctly.  If you cannot then
>>>>the linux box is not acting as a router and it should be.
>>>
[snip]
>>>Do not aplogise for being a newbie as all of us in this list were new at one 
>>>stage or another. I have managed to stuff things up very well now, after 
>>>playing around with XP on both machines. I need to reinstall XP on this dual 
>>>boot machine, however on linux I can ping 192.168.0.2 but cannot ping 
>>>192.168.0.1 from the downstairs XP. No point in looking to net when I cannot 
>>>reach this machine. 
>>>
>>>I have used another nic on the downstairs machine, also got another cable.
>>>No go.
>>>
>>>If I can ping one way why not the other ?

I am not sure what is going on.  Just to clarify some basics; each card 
in a machine needs its own ip address, ideally, each card should be on 
its own subnet.  (that may not be a requirement but it sure makes things 
easier to administer.  It also sounds like what you have.)

I am not certain, but the iptables script that David B. sent should do 
the routing.  I can't put my finger on it exactly but it sounds to me as 
though the linux box is still not working correctly.  If the XP box can 
be pinged it means the protocol is setup correctly (if not compleatly) 
and loaded.  Ping seems to work from the XP box (it doesn't error out) 
but gets lost somewhere.  I am not convinced it is getting lost in the 
XP layers.  That leads me back to the linux box not behaving like you 
want it to.

My own experience is that I could never get the linux boxes to route 
correctly when I tried what you are doing.  I found it easier for my 
peace of mind and blood pressure to invest in a router (SMC) and share 
the connection that way.  Linux or windows is just a dhcp client and 
only the router cares.  YMMV

     -- Alma