Unsecure passwords

[Pangeia <pangeia @ cdsid . com . br>]

Hello,

	I'm configuring the following scenario:

	
	SCO UNIX 1 ------------ Dedicated Line ------- SCO UNIX 2
           |
           |
        Access Server
	with 8 ports
           |
           |
        8 users using Dial Line PPP


	Well, 

	The PPP users will have access to SCO UNIX 1 and 2. They will
dial to Access Server and usage a PPP conection, that is, SCO UNIX 1
looks like an ISP.

	I know that some users write all the procedures needed to
make a connection, including passwords, on a paper at a "clean way".

	So, what can I use to only allow connections from the
"trusted machine" at users work and deny connections from other
machines with stolen passwords? Call back is a good solution?
There are any firewall that can help me with this kind of problem
(maybe with any extra authentication process at server and client)?

	Thanks,


		Leonardo Bentes
		Pangeia Informatica