News Group Posts

internet connectivity firewalls

From: Tony Lawrence <tony@pcunix.com>
Subject: Re: Looking for advice on internet connectivity
Date: Wed, 23 Oct 2002 14:53:58 -0400

Abid Khan wrote:
> Hello,
> 
> I have a client using OpenServer 5.0.5 fully patched for Medical
> practice managemnet and accounting application, they have 7 Windows
> 98/2000 work stations connected to the SCO box through a SMC hub and
> using FacetWin to connect, everything is working great, now they would
> like to have internet connectivity for Windows based machines, DSL is
> not available in there area so I am thinking about ISDN 128K, my real
> concern is to keep SCO box hidden from the outside world, so please
> advise how can I do that, do I need a dynamic or static IP's from the
> ISP, what kind of router/modem should I use, I have Ascend P75 in
> stock but open for suggessions.

Yes, the firewall should be a separate box or device.

I know nothing about Ascend, sorry.  I prefer a Linux box myself- the 
E-Smith referenced at http://aplawrence.com/esmith.html is something 
that works very well and can be totally free- your only cost is the 
hardware to run it on unless you want support or its other features 
(virus scanning, web access control etc.)  The reason I prefer this sort 
of solution is that it is software- the minute a vulnerability is found 
you can fix it yourself rather than waiting for Ascend or whoever to 
produce a new bios.  Such a setup also has the flexibilty to add your 
own customization: you needs an IDS, add Snort, etc.  You don't have to 
depend on someone else to give you whatever it is you need or want.

Not that I'm adverse to appliance style boxes.  I don't mind using a 
cheap Dlink or whatever as the first blockage to the outside world- I 
just want to have more behind it- like the E-Smith as another firewall 
and then not forgetting to lock up the SCO box just as though it were 
sitting unprotected.  The same care should be taken with the Windows 
boxes, thought sometimes that's a harder thing to do politically. 
Still, anything you can do can only help.

It never hurts to set up different kinds of watchdogs.  One may be 
sorely tempted by a hunk of raw meat when the next one in line is not. 
The sad fact is that if someone really wants you badly enough, they'll 
find a way through anything given enough motivation and time. 
Therefore, the more different obstacles you can put in their way the 
better.  Of course, someone once refuted that by saying "what if one of 
your watchdogs is easily corrupted and will help you get by all the 
others once it is compromised?"  I suppose he has a small point there 
but I still think you are better off with multiple levels of armor and 
no unnecessary services running even if something else is supposedly 
protecting it.  For example, if you don't need ftp, you should 
absolutely shut it off, but you should also filter it off both at the 
firewall(s) AND at the server just in case somebody accidentally turns 
it back on.  Further, services should be configured for the least 
dangerous access possible; telnet shouldn't allow root logins etc.

One bit that I often advise but is seldom followed: last person out at 
night disconnects the Internet.  An unconnected system can't be hacked 
while it's disconnected.  At my office, when I shut off the lights, the 
routers go dead..but that may not work for everyone.

-- 


Tony Lawrence
Unix/Linux Support Tips, How-To's, Tests and more: http://aplawrence.com
Free Unix/Linux Consultants list: http://aplawrence.com/consultants.html

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