
		    	Filter 2.0 ALPHA

Filter (FILTER.EXE) is the part of Drawbridge that runs on a PC and actually
performs the packet filtering. It takes full control of the PC once
started and cannot be used in conjunction with any other software.
DOS 5.0 is recommended. I haven't been able to get NDIS drivers
to work under DOS 6.22 (though I haven't tried to find out what the
problem was either.)

System Requirements
-------------------

Filter is a program written in ANSI C and Intel assembly language, and
compiled with Borland C++ 4.02 and Borland's Turbo Assembler 4.0.  It
will run on 386 class PC's and higher. It requires at least 2MB of
memory since it now uses XMS memory. 486 class machines and higher are
recommended for performance.

The previous versions of FILTER.EXE were coded to use only the
Elite16 (8013) series of ethernet cards from SMC. This release now
interfaces to cards using the NDIS 2.01 API. Any card that has a DOS
NDIS 2.01 driver can be used. Two cards are needed for Filter; one
interfaces to the internal network while the other interfaces to the
external network.

NOTE! The drivers for the cards *must* support promiscuous mode and
*must* allow you to configure the driver to support two cards in one
PC. Be careful to confirm this before you settle on any adapters. Some
adapters do not support these features.

An executable version of Filter is supplied along with the source
code. If you wish to examine, modify or compile the code yourself you
will need Borland C++ 4.02 (or higher) and Borland Turbo Assemmbler.
The makefile has been included. The compiling process should go
quietly.

System Setup
------------

First, before you settle on to certain cards make sure that the driver
will allow you to support two ethernet cards in a PC. If you cannot do
this then you will not be able to use these cards with Filter.

Next, configure your config.sys to load the NDIS Protocol Manager and
the driver for your cards. (This distribution of Drawbridge includes
the NDIS 2.01 tool ZIP file, a sample protocol.ini file and a sample
config.sys file.) Also enable HIMEM.SYS in your config.sys. This
enables XMS which is used by Filter. It also allows you to load DOS
high which I highly recommend.

Next, configure your protocol.ini file. All of the configuration for
Filter except for the password is in this file. The configuration
information is documented in the sample protocol.ini file that is
included. Note that all management occurs over IP now so you must
allocate and assign an IP address for Filter. Also, Filter does not
listen to ICMP redirects so choose your default gateway carefully.

Now create an autoexec.bat file that runs netbind.exe and then starts
filter.exe. I typically put filter in its own directory and cd to it
before starting it up. An example autoexec.bat file is included.

If you wish Filter to be securely managable immediately, then create a
file called PASSWORD in the same directory that will be the current
directory when Filter starts. Put an eight character white space
delimited password on the first line of this file.

Now you should be set to go.

NOTE: You should burn in a PC configuration before you start using it.
      You should also arrange for appropriate cooling and power for
      the PC before installing it. You may also want to have an extra 
      fully configured and tested PC as a backup in case of failures

Note that if you do not put Filter in the root directory, then you
should put a cd command to that directory in autoexec.bat since Filter
will look for files to load in the current working directory.

Using Filter
------------

Once you have configured and booted Filter, all management activity
occurs on the fm host. If you do not wish to use the management
software you can just take the output files from fc (using the byte
reversal switch) and then copy them to the same directory on the
PC that Filter is located.

To halt Filter once it is running, just go to the keyboard and type
a '$'. This will cause Filter to exit and return you to the DOS
prompt.  If you never intend to access the PC physically once it
is installed and if your PC's BIOS supports it, you may be able to
remove the monitor, monitor card and keyboard.  If you do leave
the keyboard attached, it is suggested that you lock the keyboard
to prevent accidental halting of Filter.

To print statistics at the console of the PC, hit the 'S' key. To
clear the statistics hit the 'C' key. Note that these are both
capital letters.
