Thanks Ken

Mine is more like the second.  I have a modem in computer A which then a 
cable goes to a hub and then to computer B.  So everything is going thru 
computer A.  If I ever get high speed I might go thru a router/firewall to 
the couple of computers, similar to the first.  I think this would be safe?

Is my home network a trusted network.  Well I trust it. Does that count. :-)

So what would the iptables configuration look like to block the xdmcp.  I kow 
very litlle about iptables.  I should learn it.  There are so many fun 
project to work on thought.  I'm going to try a diskless workstation 
eventually.  It's one of those things where I can say I've done that.  

Your diagrams were very helpfull. 

Thanks
Tim


On Friday 14 May 2004 12:47 am, you wrote:
> Hi.  I'll try to answer your questions in a way that makes sense:
>
> On Thursday 13 May 2004 21:45, Timothy Bolz wrote:
> > If X is unsafe over the internet is it safe on a trusted
> > network (for instance my couple of computers).  Can I get on
> > the internet  or is it unsecure.  Would I run some iptable
> > scripts to block anything?
>
> This is a question that could have a rather long answer, depending
> on how your home network is set up.
>
> First of all, by definition everything is safe on a trusted
> network.  But I question whether your home network is actually a
> trusted network.
>
> How are you connecting to the Internet?  If you actually have
> three devices on your home network -- two computers and a
> broadband router/modem/whatever, as in this extremely crude
> drawing which looks fine on my screen but is probably a mess on
> everyone else's:
>
>                               (Internet)
>
>  ___________          ____|_          __________
>
> | Computer A |-----------| Hub  |-------------| Computer B |
>
>  --------------------         ---------               ------------------
>
> -- then it isn't a trusted network and there is no way you can
> safely run X sessions over it without adding a firewall between
> "hub" and "Internet".
>
> If, on the other hand, only one of the computers connects to the
> Internet, like this:
>
>       (Internet)
>
> _________|__                                  __________
>
> | Computer A |--------------------------------| Computer B |
>
>  --------------------                                 ------------------
>
> (this means that Computer A has two network interfaces: one
> Ethernet card to connect to computer B, and some different device
> such as a telephone modem or a second Ethernet card to connect to
> the outside) -- then you can safely run X sessions over the
> internal LAN as long as you set up your iptables configuration on
> Computer A correctly.
>
> > If this would be unsecure how about the Linux Terminal Server
> > Project?
>
> Same exact issue.  For what it's worth, LTSP is normally
> configured like the second drawing above with the server having
> two network interfaces (one for the outside world and one for the
> internal, private LAN).  As long as its firewall is set up
> correctly, it is reasonably safe.
>
> But LTSP is normally configured to use one central server with one
> or more weak/slow/old workstations attached, not a "log into
> either one from the other" configuration, which is what I believe
> you want.
>
> I hope this helps.
>
> Ken
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