ipfw rule deletion

[Aaron Dalton]

I am using Doorman (http://doorman.sourceforge.net)as a port knocking
daemon and I need to write a short script that adds and deletes rules to
the ipfw firewall.  I can add them just fine, but I can't find the best
way to delete them.  Is the only way to specify the exact rule number?
Below is the add script itself.  Thanks for your help!

#!/bin/sh
#
#  file "ipfw_add"
#  Sample firewall-add script, called by "doormand".
#  This example can be used by systems which use ipfw.
#
#  Called with five arguments:
#
# $1 : name of the interface (e.g. eth0)
# #2 : source IP; i.e. dotted-decimal address of the 'knock' client
# $3 : source port; when this script is called for the first time
#      for a connection (man 8 doormand), this argument will be set
#      to a single "0" (0x30) character.  This means that the source
#      port is not yet known, and a broad rule allowing any source
#      port is required.
# $4 : destination IP; that is, the IP address of the interface
#      in argument 1.
# $5 : The port number of the requested service (e.g. 22 for ssh, etc.)
#
#
if [ $3 = 0 ]
then
    ipfw  add    allow log tcp   from $2      to $4 $5   in  setup
keep-state
else
    ipfw  add    allow log tcp   from $2 $3   to $4 $5   in  setup
keep-state
fi

err=$?

if [ $err = 0 ]
then
    echo 0
else
    echo $err 3  The firewall_add script sez: "Dang."
fi


-- 
Aaron Dalton
acdalton at ucalgary.ca
PGPKeyID# 0x65AB5571