The firewall scripts files
The tool ipchains allows you to set up firewalls, IP masquerading, etc. Ipchains talks to the kernel and tells it what packets to filter. Therefore all your firewall setups are stored in the kernel, and thus will be lost on reboot. To avoid this, we recommend using the System V init scripts to make your rules permanent. To do this, create a firewall script file like shown below in your 7etc/rc.d/init.d/” directory for each servers you have. Of course, each server has different services to offer and needs a different firewall setup. For this reason, we provide you three different firewall settings, which you can play with, and examine to fit your needs. Also I assume that you have a minimum knowledge on how filtering firewalls and firewall rules works.
Configuration of the “/etc/rc.d/init.d/firewall” script file for the Web Server
This is the configuration script file for our Web Server. This configuration allows unlimited traffic on the Loopback interface, ICMP, DNS Caching and Client Server (53), SSH Server (22), HTTP Server (80), HTTPS Server (443), SMTP Client (25), FTP Server (20, 21), and OUTGOING TRACEROUTE requests by default.
If you don’t want some services listed in the firewall rules files for the Web Server that I make ON by default, comment them out with a “#” at the beginning of the line. If you want some other services that I commented out with a “#”, then remove the “#” at the beginning of those lines.
Create the firewall script file (touch /etc/rc.d/init.d/firewall) on your Web Server and add:
#!/bin/sh #
# Last modified by Gerhard Mourani: 04-25-2000
# Copyright (C) 1997, 1998,1999 Robert L. Ziegler
# Permission to use, copy, modify, and distribute this software and its
# documentation for educational, research, private and non-profit purposes,
# without fee, and without a written agreement is hereby granted.
# This software is provided as an example and basis for individual firewall
# development. This software is provided without warranty.
#
# Any material furnished by Robert L. Ziegler is furnished on an
# “as is” basis. He makes no warranties of any kind, either expressed
# or implied as to any matter including, but not limited to, warranty
# of fitness for a particular purpose, exclusivity or results obtained
# from use of the material.
#
# Invoked from /etc/rc.d/init.d/firewall.
# chkconfig: - 60 95
# description: Starts and stops the IPCHAINS Firewall \
# used to provide Firewall network services.
# Source function library.
. /etc/rc.d/init.d/functions
# Source networking configuration.
. /etc/sysconfig/network
# Check that networking is up.