🚀 go-pugleaf

I am looking for a Linux guru for some quick answers to questions about 
firewalls and proxy servers.

I run a part time consulting business specializing  in setting up small (5-50 
user) Novell, Windows, and Unix networks  networks.  In my day job I manage a 
mixed 9000+ user network.  A friend put me on to Linux as a cheaper and 
possibly better alternative to some of my existing configurations.  He showed 
me his small Linux server and it really impressed me.  It looked like a good 
rival to $5,000 worth of SCO Open Server.  Unfortunately my friend could not 
answer some technical questions.

Nearly all of my customers are getting connected to the Internet.  Most only 
have dial on demand connectivity, but some have leased lines.  One of my 
favorite configurations is to user a proxy server to connect the entire office 
through a single ISP connection.  This way the private IP addresses on the 
network are not visible on the Internet.  This can also be done with some 
firewalls.  Is there such a product available for Linux? If so where can I get 
it?

Sincerely,
Fred Hebert.