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#!/bin/sh
#
# rc.firewall-2.6
#FWVER=0.75
#
# Initial SIMPLE IP
Masquerade test for 2.4.x kernels
# using IPTABLES.
#
# Once IP Masquerading
has been tested, with this simple
# ruleset, it is highly
recommended to use a stronger
# IPTABLES ruleset
either given later in this HOWTO or
# from another
reputable resource.
#
#
#
# Log:
# 0.75 - Added more kernel modules to the comments
section
# 0.74 - the ruleset now uses modprobe vs. insmod
# 0.73 - REJECT is not a legal policy yet; back to
DROP
# 0.72 - Changed the default block behavior to
REJECT not DROP
# 0.71 - Added clarification that PPPoE users need
to use
# "ppp0" instead of
"eth0" for their external interface
# 0.70 - Added commented option for IRC nat module
# - Added additional use of
environment variables
# - Added additional formatting
# 0.63 - Added support for the IRC IPTABLES module
# 0.62 - Fixed a typo on the MASQ enable line that
used eth0
# instead of $EXTIF
# 0.61 - Changed the firewall to use variables for
the internal
# and external interfaces.
# 0.60 - 0.50 had a mistake where the ruleset had a
rule to DROP
# all forwarded packets but
it didn't have a rule to ACCEPT
# any packets to be forwarded
either
# - Load the ip_nat_ftp and
ip_conntrack_ftp modules by default
# 0.50 - Initial draft
#
echo -e "\n\nLoading simple rc.firewall version $FWVER..\n"
# The location of the iptables and kernel module programs
#
# If your Linux distribution came with a copy of iptables,
# most likely all the programs will be located in /sbin. If
# you manually compiled iptables, the default location will
# be in /usr/local/sbin
#
# ** Please use the "whereis iptables" command to figure out
# ** where your copy is and change the path below to reflect
# ** your setup
#
IPTABLES=/sbin/iptables
DEPMOD=/sbin/depmod
MODPROBE=/sbin/modprobe
#Setting the EXTERNAL and INTERNAL interfaces for the network
#
# Each IP Masquerade network needs to have at least one
# external and one internal network. The external network
# is where the natting will occur and the internal network
# should preferably be addressed with a RFC1918 private address
# scheme.
#
# For this example, "eth0" is external and "eth1"
is internal"
#
#
# NOTE: If this doesnt EXACTLY fit your configuration, you must
# change the EXTIF or INTIF variables above.
For example:
#
# If you are a PPPoE or analog modem
user:
#
#
EXTIF="ppp0"
#
#
TEQLIF="teql0"
EXTIF="eth0"
EXTIF2="eth1"
EXTIF3="eth3"
INTIF="eth2"
echo " TEQL Interface: $TEQLIF"
echo " External Interface: $EXTIF"
echo " External Interface: $EXTIF2"
echo " External Interface: $EXTIF3"
echo " Internal Interface: $INTIF"
#======================================================================
#== No editing beyond this line is required for initial MASQ testing ==
echo -en " loading modules: "
# Need to verify that all modules have all required dependencies
#
echo " - Verifying that all kernel modules are ok"
$DEPMOD -a
# With the new IPTABLES code, the core MASQ functionality is now either
# modular or compiled into the kernel. This HOWTO shows ALL IPTABLES
# options as MODULES. If your kernel is compiled correctly, there is
# NO need to load the kernel modules manually.
#
# NOTE: The following items are listed ONLY for informational reasons.
# There is no reason to manual load these modules
unless your
# kernel is either mis-configured or you
intentionally disabled
# the kernel module autoloader.
#
# Upon the commands of starting up IP Masq on the server, the
# following kernel modules will be automatically loaded:
#
# NOTE: Only load the IP MASQ modules you need. All current IP
MASQ
# modules are shown below but are commented out
from loading.
# ===============================================================
echo "----------------------------------------------------------------------"
#Load the main body of the IPTABLES module - "iptable"
# - Loaded automatically when the "iptables" command is
invoked
#
# - Loaded manually to clean up kernel auto-loading timing issues
#
echo -en "ip_tables, "
$MODPROBE ip_tables
#Load the IPTABLES filtering module - "iptable_filter"
# - Loaded automatically when filter policies are activated
#Load the stateful connection tracking framework - "ip_conntrack"
#
# The conntrack module in itself does nothing without other specific
# conntrack modules being loaded afterwards such as the
"ip_conntrack_ftp"
# module
#
# - This module is loaded automatically when MASQ functionality is
# enabled
#
# - Loaded manually to clean up kernel auto-loading timing issues
#
echo -en "ip_conntrack, "
$MODPROBE ip_conntrack
#Load the FTP tracking mechanism for full FTP tracking
#
# Enabled by default -- insert a "#" on the next line to deactivate
#
echo -en "ip_conntrack_ftp, "
$MODPROBE ip_conntrack_ftp
#Load the IRC tracking mechanism for full IRC tracking
#
# Enabled by default -- insert a "#" on the next line to deactivate
#
echo -en "ip_conntrack_irc, "
$MODPROBE ip_conntrack_irc
#Load the general IPTABLES NAT code - "iptable_nat"
# - Loaded automatically when MASQ functionality is turned on
#
# - Loaded manually to clean up kernel auto-loading timing issues
#
echo -en "iptable_nat, "
$MODPROBE iptable_nat
#Loads the FTP NAT functionality into the core IPTABLES code
# Required to support non-PASV FTP.
#
# Enabled by default -- insert a "#" on the next line to deactivate
#
echo -en "ip_nat_ftp, "
$MODPROBE ip_nat_ftp
#Loads the IRC NAT functionality into the core IPTABLES code
# Required to support NAT of IRC DCC requests
#
# Disabled by default -- remove the "#" on the next line to
activate
#
echo -e "ip_nat_irc"
$MODPROBE ip_nat_irc
echo "----------------------------------------------------------------------"
# Just to be complete, here is a partial list of some of the other
# IPTABLES kernel modules and their function. Please note that most
# of these modules (the ipt ones) are automatically loaded by the
# master kernel module for proper operation and don't need to be
# manually loaded.
# --------------------------------------------------------------------
#
# ip_nat_snmp_basic - this module allows for proper NATing of
some
#
SNMP traffic
#
# iptable_mangle - this target allows for packets
to be
#
manipulated for things like the TCPMSS
#
option, etc.
#
# --
#
# ipt_mark - this target marks a given
packet for future action.
#
This automatically loads the ipt_MARK module
#
# ipt_tcpmss - this target allows to
manipulate the TCP MSS
#
option for braindead remote firewalls.
#
This automatically loads the ipt_TCPMSS module
#
# ipt_limit - this target allows for packets
to be limited to
#
to many hits per sec/min/hr
#
# ipt_multiport - this match allows for targets within a
range
#
of port numbers vs. listing each port individually
#
# ipt_state - this match allows to catch
packets with various
#
IP and TCP flags set/unset
#
# ipt_unclean - this match allows to catch packets
that have invalid
#
IP/TCP flags set
#
# iptable_filter - this module allows for packets to be DROPped,
#
REJECTed, or LOGged. This module automatically
#
loads the following modules:
#
#
ipt_LOG - this target allows for packets to be
#
logged
#
#
ipt_REJECT - this target DROPs the packet and returns
#
a configurable ICMP packet back to
the
#
sender.
#
echo -e " Done loading modules.\n"
#CRITICAL: Enable IP forwarding since it is disabled by default since
#
# Redhat Users: you may try
changing the options in
#
/etc/sysconfig/network from:
#
#
FORWARD_IPV4=false
#
to
#
FORWARD_IPV4=true
#
echo " Enabling forwarding.."
echo 1 > /proc/sys/net/ipv4/ip_forward
# Dynamic IP users:
#
# If you get your IP address dynamically from SLIP, PPP, or DHCP,
# enable this following option. This enables
dynamic-address hacking
# which makes the life with Diald and similar programs much
easier.
#
echo " Enabling DynamicAddr.."
echo "1" > /proc/sys/net/ipv4/ip_dynaddr
# Enable simple IP forwarding and Masquerading
#
# NOTE: In IPTABLES speak, IP Masquerading is a form of SourceNAT
or SNAT.
#
# NOTE #2: The following is an example for an internal LAN
address in the
# 192.168.0.x network with a
255.255.255.0 or a "24" bit subnet mask
# connecting to the Internet on
external interface "eth0". This
# example will MASQ internal traffic
out to the Internet but not
# allow non-initiated traffic into
your internal network.
#
#
# ** Please change the above network
numbers, subnet mask, and your
# *** Internet connection interface name to
match your setup
#
#Clearing any previous configuration
#
# Unless specified, the defaults for INPUT and OUTPUT is ACCEPT
# The default for FORWARD is DROP (REJECT is not a valid policy)
#
echo " Clearing any existing rules and setting default
policy.."
$IPTABLES -P INPUT ACCEPT
$IPTABLES -F INPUT
$IPTABLES -P OUTPUT ACCEPT
$IPTABLES -F OUTPUT
$IPTABLES -P FORWARD DROP
$IPTABLES -F FORWARD
$IPTABLES -t nat -F
echo " FWD: Allow all connections OUT and only existing and
related ones IN"
$IPTABLES -A FORWARD -i $TEQLIF -o $INTIF -m state --state
ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -i $EXTIF -o $INTIF -m state --state ESTABLISHED,RELATED
-j ACCEPT
$IPTABLES -A FORWARD -i $EXTIF2 -o $INTIF -m state --state
ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -i $EXTIF3 -o $INTIF -m state --state
ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -i $INTIF -o $TEQLIF -j ACCEPT
$IPTABLES -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT
$IPTABLES -A FORWARD -i $INTIF -o $EXTIF3 -j ACCEPT
$IPTABLES -A FORWARD -i $INTIF -o $EXTIF2 -j ACCEPT
$IPTABLES -A FORWARD -j LOG
echo " Enabling SNAT (MASQUERADE) functionality on
$TEQLIF"
$IPTABLES -t nat -A POSTROUTING -o $TEQLIF -j MASQUERADE
$IPTABLES -t nat -A POSTROUTING -o $EXTIF -j MASQUERADE
$IPTABLES -t nat -A POSTROUTING -o $EXTIF2 -j MASQUERADE
$IPTABLES -t nat -A POSTROUTING -o $EXTIF3 -j MASQUERADE
iptables -I FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS
--clamp-mss-to-pmtu
echo -e "\nrc.firewall-2.6 v$FWVER done.\n"
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