network problem: internet sharing

[Alma J Wetzker]

Matt, No offense taken.  I was just getting a col box on the net (I 
mostly do development so the net wasn't critical) and I wanted to share 
the dialup connection with other machines on the home network.  All the 
FAQ's and howto's told me how to setup ipchains.  So I went and found 
ipchains and loaded it up. nothing ever worked right.  I do know IP 
networking but I don't know *nix real well.  I finally asked for help 
and was told, bluntly, to pay attention and use iptables.  (See 'if 
linux were cars')  After reading up on iptables and fiddling some more 
it still was not working the way I wanted and 3 - 4 weeks had gone by. 
A $60 SMC router will handle modem dialout, act as a print server and 
act as a dhcp server.  As far as I am concerned, that fixes the problem 
and I get what I want from the network.  I  still don't know what was 
not setup correctly on my part but I don't care enough to find out.  (I 
really don't have the time.)

With Keith's setup, I was concerned that the network cards in the linux 
box might not be routing across each other.  I like to setup a separate 
logical network segment for each card if only for ease of maintenance. 
For instance:
     eth0    192.168.0.1    nm 255.255.255.0
     eth1    192.168.1.1    nm 255.255.255.0

My background is CPM, DOS and Novell along with some embedded stuff.  I 
have tended to do software links between applications that are not 
supposed to talk to each other.  Doing system admin stuff is new to me 
and not terribly exciting for its own sake.  I know I don't fit in but I 
am learning alot.

     -- Alma

> Matthew Carpenter <matt at eisgr.com>
> Wed, 23 Jul 2003 12:23:18 -0400
> 
> I'd be interested in hearing your experience.  My company has invested a lot
> into Linux as a firewall/router/NAT device because we can depend on them
> better than just about anything else available.  Short of Hardware failure,
> Linux firewalls/routers/NAT devices are one of the most powerful and reliable
> on the market, being able to do complex firewalling, IDS/IDP, NAT (both
> directions), reporting, and much more.  
> 
> The only times I have found Linux not function well in this roll has been
> resulting from a lack of basic education.  The workstations behind it weren't
> configured for IP or there wasn't a DHCP server or the DHCP configuration
> wasn't handing out a default route correctly.  
> 
> No offense to you, Alma... I know I must be sounding like a biggot at the
> moment (sounding the trumpet while on the Linux list and all), but most
> problems I've found have been lack of knowledge about how a TCP/IP network
> works, including configuration and routing.  And Microsoft tries to automate
> it... but AUTO is a four-letter word, because AUTO only works part of the
> time.  And the AUTO methods tend to make you not consider some potential
> problem areas because they work sometimes.  While I'm not sure what is going
> on at Keith's I have to say that in the event of "random" or "inconsistent"
> issues, most problems I've dealt with have been a Windows problem.
> My biggest unknown here is Mandrake, since Mandrake is attempting to be a
> Microsoft competitor, they may be attempting some "automated" stuff.
> 
> I'm not sure whether this was covered or not, but if you have the XP box set
> to dynamic, you need a DHCP server.  If it is hard-set to 192.168.1.2, it
> needs to have the correct netmask (most often chosen as 255.255.255.0 but if
> generated by network class, it could be 255.255.0.0), Default Gateway of
> 192.168.1.2, and DNS servers need to be set to whatever the Linux box is being
> handed in DHCP.  Otherwise, you can point to mine: 69.33.10.245 and
> 69.33.10.246.
> 
> Again, no offense to anyone here.
> Thanks,
> Matt