#!/bin/sh
#
# Written by Dominic Hargreaves
#
# This script is released without copyright. It is, or is based on, code from
# <http://www.larted.org.uk/~dom/computing/code/iptfirewall>.
#
# It is designed to be a single host, stateful, and default deny firewall.
#
# The commented out entries are examples which may or may not be relevant
# in your environment.
#
# If you don't have a ulogd configured, change ULOG to LOG in the shell
# variable $LOGTYPE, and logs will appear in dmesg instead.
#
# IMPORTANT NOTICE: By default this script will block *all* incoming
# connections. This means that you *must* make sure you enable incoming
# ssh, or the emergency host access, if you are implementing this over an
# ssh connection.

PATH=/sbin

# Shortcuts
IN="iptables -A INPUT -m state --state"
OUT="iptables -A OUTPUT -m state --state"

# Defs
#LOCALNET="10.1.1.0/24"
#EMERGENCY_HOST="163.1.2.4"
LOGTYPE="ULOG"

# Flush rules
iptables -F

# Emergency access
#iptables -A INPUT -p tcp -s $EMERGENCY_HOST --dport 22 -j ACCEPT
#iptables -A OUTPUT -p tcp -d $EMERGENCY_HOST --sport 22 -j ACCEPT

# Set policies
iptables -P FORWARD DROP
iptables -P INPUT DROP
iptables -P OUTPUT DROP

# Delete old user-defined tables
iptables -X

# Set up drop and log table
iptables -N DLOG
iptables -A DLOG -j $LOGTYPE
iptables -A DLOG -j DROP

# Block and log bogons
iptables -A INPUT -s 127.0.0.0/8 ! -i lo -j DLOG

# Block invalid packets
$IN INVALID -j DLOG

# Allow outbound connections to be made
$OUT NEW,RELATED,ESTABLISHED -j ACCEPT
$IN RELATED,ESTABLISHED -j ACCEPT

# Allow everything to/from localhost
$IN NEW -i lo -j ACCEPT

# Allow incoming ping
#$IN NEW -p icmp --icmp-type echo-request -j ACCEPT

# Allow incoming services to all
#$IN NEW -p tcp -m multiport --dports ssh,www -j ACCEPT 
#$IN NEW -p udp -m multiport --dports ntp -j ACCEPT

# Allow mail from our MX
#$IN NEW -p tcp --dport smtp -s 10.1.3.1 -j ACCEPT

# Allow smb from our local network
#$IN NEW -p tcp -m multiport --dports netbios-ns,netbios-dgm,netbios-ssn,microsoft-ds -s $LOCALNET -j ACCEPT
#$IN NEW -p udp -m multiport --dports netbios-ns,netbios-dgm,netbios-ssn -s $LOCALNET -j ACCEPT

# Reject kindly to prevent timeouts
$IN NEW -p tcp --dport auth -j REJECT --reject-with tcp-reset

# Drop these now to prevent unnecessarily logging
iptables -A INPUT -m pkttype --pkt-type broadcast -j DROP

# Log everything else for diagnostics
# (note that policies for INPUT,OUTPUT,FORWARD are DROP)
iptables -A INPUT -j $LOGTYPE
iptables -A OUTPUT -j $LOGTYPE
iptables -A FORWARD -j $LOGTYPE