Great Circle Associates Firewalls
(April 1995)
 

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Subject: Secure Modem Pool
From: se @ adv . sbc . sony . co . jp (Steve England)
Date: Mon, 24 Apr 95 18:13:18 BST
To: firewalls @ greatcircle . com


Questions:

Are there generally recommended way(s) in which to setup a 
pool of modems for dialin (possibly dialback) capability whilst 
remaining secure ? 

Brief background:
SLIP/PPP are not involved, & the users have DOS pc's at home, 
connecting into a SunOS 4.x box - this small network is soon to be
connected via a leased line to a larger main network - which 
will supply the inet connection & will have the firewall
setup - our only concern here are is securing the modems at the 
small site.

The following thoughts have occured to me - please comment/criticise
constructively.

1. Recently i have heard that dialback modems arent as secure as
   once (?) thought. Does anyone have any experiences/war-stories/
   hard facts on this ?
2. I have heard of a device that can attach to the phone network &
   monitor the target phone number & log data (passwords ?) from it
   for later re-use. Would Bellcore S/Key be strong enough to defeat this
   in as much as, "so what if you see the password its only valid once".
3. Possibly using a low-end cisco with modem support, alternatively a
   telebit netblazer, but i've heard there's problems with its *strange*
   optimisation with the rules you supply it. Any preferences/why ?
4. Would it be a good idea to screen the modems off into another subnet
   & monitor that net for dialin attempts ?


Thanks & Regards

Steve


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