[NTLUG:Discuss] Getting out past a firewall easiest

[Kipton Moravec]

At 10:23 AM 6/5/03, Jack Snodgrass wrote:
>On Thu, 05 Jun 2003 08:36:46 -0700, Kipton Moravec wrote:
>
> > I am developing a system that will be a sophisticaded appliance for 
> certain
> > businesses.
> >
> > Part of the system monitors other equipment and if an error occurs sends
> > some sort of message to a server on the Internet.  In addition I want 
> it to
> > periodically check in to get software updates automatically.
> >
>
>
>First of all, make sure that the company that you are doing
>work for knows this and agrees to this. If you were an evil
>person, you could do a lot of harm to their internal network
>if they allow you to do this and you wanted to do evil deeds.
>If you try and do this without them agreeing up front, you
>may be in for some serious trouble.
>

They are paying us a monthly fee for the monitoring so yes they know what 
we are doing, and we remind them monthly with our invoice. :)

>Now that that is said... you don't know what ports will be
>open for external connections. Some companies let pretty
>much any outgoing connections. Other companies block pretty
>much everything.

Since these are small businesses (restaurants) I expect most will have some 
kind of off the shelf DSL or Cable Modem router and nothing very 
sophisticated. But one never knows what else may be out there which is why 
I asked the question.

>You'll need to design your software so that it can make an
>outgoing socket connection via different ports. It will have
>to try them out until it gets a good connection. Don't assume
>that everyone has port 80 open ( web ) becuase they may make
>their users use a proxy server and only the proxy server
>can access port 80 outside of the company. Many companies won't
>let users send email ( port 25 ) to anything other than the
>local mail server that can then send mail via port 25.

We were looking at port 80 as our first try.  Did not think of trying 
different ports. I figured if port 80 was closed then the rest would be 
closed also. Thanks for the suggestion. If port 80 was closed, what other 
ports would you recommend trying?

Is there a "generic" way to hook up to a Proxy Server or could each one be 
different?  Where should I go to read up more on dealing with a proxy server?

>On your server side, you'll have to set up your server so
>that it listens to multiple ports, detects an incomming
>connection from your client and is able to handle it on
>any port.

Not a problem.  We will have a dedicated computer for just this task on the 
server side.

>jack
>
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