
		    	Filter 1.0 (Beta Release)

Filter is the part of Drawbridge that runs on a 486 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.

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

Filter is a program written in ANSI C, and compiled with Borland's
Turbo C++ 3.0.  It will run on 386 class PC's with 1MB of memory,
and 5MB of hard disk space, but 486 class machines are recommended
for performance.  Memory over 1MB is not used by the filter program,
although more memory may be needed to modify and recompile the
program with Turbo C++.

Filter is currently coded to use only the Elite16 (8013) series of
ethernet cards from SMC. Future versions may add support for more
cards. Two cards are needed for Filter; one interfaces to the
internal network while the other interfaces to the external network.

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 Turbo C++ 3.0.  The make file and project
file have been included. The compiling process should go quietly
except for two warnings about an unused parameter in a function
definition.

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

The two ethernet cards cards must be set at memory locations
0xD000:0x0000/port 0x280 and 0xCC00:0x0000/port 0x300. The card at
D000:0000 is considered the "internal" network card and the card
at CC00:0000 is considered the "external" network card. You must
keep track of which is physically which and install the cabling
correctly.  Be careful and also configure the cards properly for
either AUI or thin net ports. You do not need to worry about the
interrupts as Filter always polls.  Depending on the model of 8013
you are using, you may need to set these configurations with jumpers,
with the ezsetup program or both.

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

Filter is an executable called FILTER.EXE and should run on most
compatibles.  You should set up the PC to have no device drivers
installed (pretty much empty config.sys) and with an autoexec.bat
that will automatically start the filter in case of power failures
or reboots from fm. Filter takes one argument which determines
which cards Filter will listen for remote fm commands on. The
invocation is:

filter [-l (inside|outside|both)]

The arguments specify which side Filter will listen to for fm management
commands. If no arguments are present then Filter will not respond to any
fm commands.

If you copy FILTER.EXE to the root directory of the hard drive on
the PC then your autoexec.bat could look like:

c:\filter.exe -l inside

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.EXE 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.

If you happen to lose your DES key on the fm host, then you must
go to the Filter and delete or replace the DES.KEY file. This will
put the filter back into insecure mode and you can install a new
key.
