Iptables - Printable Version

Code:
#!/bin/sh

#

# Generated iptables firewall script for the Linux 2.4 kernel

# Script generated by Easy Firewall Generator for IPTables 1.15

# copyright 2002 Timothy Scott Morizot

# 

# Redhat chkconfig comments - firewall applied early,

#                             removed late

# chkconfig: 2345 08 92

# description: This script applies or removes iptables firewall rules

# 

# This generator is primarily designed for RedHat installations,

# although it should be adaptable for others.

#

# It can be executed with the typical start and stop arguments.

# If used with stop, it will stop after flushing the firewall.

# The save and restore arguments will save or restore the rules

# from the /etc/sysconfig/iptables file.  The save and restore

# arguments are included to preserve compatibility with

# Redhat's or Fedora's init.d script if you prefer to use it.



# Redhat/Fedora installation instructions

#

# 1. Have the system link the iptables init.d startup script into run states

#    2, 3, and 5.

#    chkconfig --level 235 iptables on

#

# 2. Save this script and execute it to load the ruleset from this file.

#    You may need to run the dos2unix command on it to remove carraige returns.

#

# 3. To have it applied at startup, copy this script to

#    /etc/init.d/iptables.  It accepts stop, start, save, and restore

#    arguments.  (You may wish to save the existing one first.)

#    Alternatively, if you issue the 'service iptables save' command

#    the init.d script should save the rules and reload them at runtime.

#

# 4. For non-Redhat systems (or Redhat systems if you have a problem), you

#    may want to append the command to execute this script to rc.local.

#    rc.local is typically located in /etc and /etc/rc.d and is usually

#    the last thing executed on startup.  Simply add /path/to/script/script_name

#    on its own line in the rc.local file.



###############################################################################

# 

# Local Settings

#



# sysctl location.  If set, it will use sysctl to adjust the kernel parameters.

# If this is set to the empty string (or is unset), the use of sysctl

# is disabled.



SYSCTL="/sbin/sysctl -w" 



# To echo the value directly to the /proc file instead

# SYSCTL=""



# IPTables Location - adjust if needed



IPT="/sbin/iptables"

IPTS="/sbin/iptables-save"

IPTR="/sbin/iptables-restore"



# Internet Interface

INET_IFACE="eth0"

INET_ADDRESS="72.55.184.44"



# Localhost Interface



LO_IFACE="lo"

LO_IP="127.0.0.1"



# Save and Restore arguments handled here

if [ "$1" = "save" ]

then

    echo -n "Saving firewall to /etc/sysconfig/iptables ... "

    $IPTS > /etc/sysconfig/iptables

    echo "done"

    exit 0

elif [ "$1" = "restore" ]

then

    echo -n "Restoring firewall from /etc/sysconfig/iptables ... "

    $IPTR < /etc/sysconfig/iptables

    echo "done"

    exit 0

fi



###############################################################################

#

# Load Modules

#



echo "Loading kernel modules ..."



# You should uncomment the line below and run it the first time just to

# ensure all kernel module dependencies are OK.  There is no need to run

# every time, however.



# /sbin/depmod -a



# Unless you have kernel module auto-loading disabled, you should not

# need to manually load each of these modules.  Other than ip_tables,

# ip_conntrack, and some of the optional modules, I've left these

# commented by default.  Uncomment if you have any problems or if

# you have disabled module autoload.  Note that some modules must

# be loaded by another kernel module.



# core netfilter module

/sbin/modprobe ip_tables



# the stateful connection tracking module

/sbin/modprobe ip_conntrack



# filter table module

# /sbin/modprobe iptable_filter



# mangle table module

# /sbin/modprobe iptable_mangle



# nat table module

# /sbin/modprobe iptable_nat



# LOG target module

# /sbin/modprobe ipt_LOG



# This is used to limit the number of packets per sec/min/hr

# /sbin/modprobe ipt_limit



# masquerade target module

# /sbin/modprobe ipt_MASQUERADE



# filter using owner as part of the match

# /sbin/modprobe ipt_owner



# REJECT target drops the packet and returns an ICMP response.

# The response is configurable.  By default, connection refused.

# /sbin/modprobe ipt_REJECT



# This target allows packets to be marked in the mangle table

# /sbin/modprobe ipt_mark



# This target affects the TCP MSS

# /sbin/modprobe ipt_tcpmss



# This match allows multiple ports instead of a single port or range

# /sbin/modprobe multiport



# This match checks against the TCP flags

# /sbin/modprobe ipt_state



# This match catches packets with invalid flags

# /sbin/modprobe ipt_unclean



# The ftp nat module is required for non-PASV ftp support

/sbin/modprobe ip_nat_ftp



# the module for full ftp connection tracking

/sbin/modprobe ip_conntrack_ftp



# the module for full irc connection tracking

/sbin/modprobe ip_conntrack_irc





###############################################################################

#

# Kernel Parameter Configuration

#

# See http://ipsysctl-tutorial.frozentux.net/chunkyhtml/index.html

# for a detailed tutorial on sysctl and the various settings

# available.



# Required to enable IPv4 forwarding.

# Redhat users can try setting FORWARD_IPV4 in /etc/sysconfig/network to true

# Alternatively, it can be set in /etc/sysctl.conf

#if [ "$SYSCTL" = "" ]

#then

#    echo "1" > /proc/sys/net/ipv4/ip_forward

#else

#    $SYSCTL net.ipv4.ip_forward="1"

#fi



# This enables dynamic address hacking.

# This may help if you have a dynamic IP address \(e.g. slip, ppp, dhcp\).

#if [ "$SYSCTL" = "" ]

#then

#    echo "1" > /proc/sys/net/ipv4/ip_dynaddr

#else

#    $SYSCTL net.ipv4.ip_dynaddr="1"

#fi



# This enables SYN flood protection.

# The SYN cookies activation allows your system to accept an unlimited

# number of TCP connections while still trying to give reasonable

# service during a denial of service attack.

if [ "$SYSCTL" = "" ]

then

    echo "1" > /proc/sys/net/ipv4/tcp_syncookies

else

    $SYSCTL net.ipv4.tcp_syncookies="1"

fi



# This enables source validation by reversed path according to RFC1812.

# In other words, did the response packet originate from the same interface

# through which the source packet was sent?  It's recommended for single-homed

# systems and routers on stub networks.  Since those are the configurations

# this firewall is designed to support, I turn it on by default.

# Turn it off if you use multiple NICs connected to the same network.

if [ "$SYSCTL" = "" ]

then

    echo "1" > /proc/sys/net/ipv4/conf/all/rp_filter

else

    $SYSCTL net.ipv4.conf.all.rp_filter="1"

fi



# This option allows a subnet to be firewalled with a single IP address.

# It's used to build a DMZ.  Since that's not a focus of this firewall

# script, it's not enabled by default, but is included for reference.

# See: http://www.sjdjweis.com/linux/proxyarp/ 

#if [ "$SYSCTL" = "" ]

#then

#    echo "1" > /proc/sys/net/ipv4/conf/all/proxy_arp

#else

#    $SYSCTL net.ipv4.conf.all.proxy_arp="1"

#fi



# The following kernel settings were suggested by Alex Weeks. Thanks!



# This kernel parameter instructs the kernel to ignore all ICMP

# echo requests sent to the broadcast address.  This prevents

# a number of smurfs and similar DoS nasty attacks.

if [ "$SYSCTL" = "" ]

then

    echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

else

    $SYSCTL net.ipv4.icmp_echo_ignore_broadcasts="1"

fi



# This option can be used to accept or refuse source routed

# packets.  It is usually on by default, but is generally

# considered a security risk.  This option turns it off.

if [ "$SYSCTL" = "" ]

then

    echo "0" > /proc/sys/net/ipv4/conf/all/accept_source_route

else

    $SYSCTL net.ipv4.conf.all.accept_source_route="0"

fi



# This option can disable ICMP redirects.  ICMP redirects

# are generally considered a security risk and shouldn't be

# needed by most systems using this generator.

#if [ "$SYSCTL" = "" ]

#then

#    echo "0" > /proc/sys/net/ipv4/conf/all/accept_redirects

#else

#    $SYSCTL net.ipv4.conf.all.accept_redirects="0"

#fi



# However, we'll ensure the secure_redirects option is on instead.

# This option accepts only from gateways in the default gateways list.

if [ "$SYSCTL" = "" ]

then

    echo "1" > /proc/sys/net/ipv4/conf/all/secure_redirects

else

    $SYSCTL net.ipv4.conf.all.secure_redirects="1"

fi



# This option logs packets from impossible addresses.

if [ "$SYSCTL" = "" ]

then

    echo "1" > /proc/sys/net/ipv4/conf/all/log_martians

else

    $SYSCTL net.ipv4.conf.all.log_martians="1"

fi





###############################################################################

#

# Flush Any Existing Rules or Chains

#



echo "Flushing Tables ..."



# Reset Default Policies

$IPT -P INPUT ACCEPT

$IPT -P FORWARD ACCEPT

$IPT -P OUTPUT ACCEPT

$IPT -t nat -P PREROUTING ACCEPT

$IPT -t nat -P POSTROUTING ACCEPT

$IPT -t nat -P OUTPUT ACCEPT

$IPT -t mangle -P PREROUTING ACCEPT

$IPT -t mangle -P OUTPUT ACCEPT



# Flush all rules

$IPT -F

$IPT -t nat -F

$IPT -t mangle -F



# Erase all non-default chains

$IPT -X

$IPT -t nat -X

$IPT -t mangle -X



if [ "$1" = "stop" ]

then

    echo "Firewall completely flushed!  Now running with no firewall."

    exit 0

fi



###############################################################################

#

# Rules Configuration

#



###############################################################################

#

# Filter Table

#

###############################################################################



# Set Policies



$IPT -P INPUT DROP

$IPT -P OUTPUT DROP

$IPT -P FORWARD DROP



###############################################################################

#

# User-Specified Chains

#

# Create user chains to reduce the number of rules each packet

# must traverse.



echo "Create and populate custom rule chains ..."



# Create a chain to filter INVALID packets



$IPT -N bad_packets



# Create another chain to filter bad tcp packets



$IPT -N bad_tcp_packets



# Create separate chains for icmp, tcp (incoming and outgoing),

# and incoming udp packets.



$IPT -N icmp_packets



# Used for UDP packets inbound from the Internet

$IPT -N udp_inbound



# Used to block outbound UDP services from internal network

# Default to allow all

$IPT -N udp_outbound



# Used to allow inbound services if desired

# Default fail except for established sessions

$IPT -N tcp_inbound



# Used to block outbound services from internal network

# Default to allow all

$IPT -N tcp_outbound



###############################################################################

#

# Populate User Chains

#



# bad_packets chain

#



# Drop INVALID packets immediately

$IPT -A bad_packets -p ALL -m state --state INVALID -j LOG \

    --log-prefix "Invalid packet: "



$IPT -A bad_packets -p ALL -m state --state INVALID -j DROP



# Then check the tcp packets for additional problems

$IPT -A bad_packets -p tcp -j bad_tcp_packets



# All good, so return

$IPT -A bad_packets -p ALL -j RETURN



# bad_tcp_packets chain

#

# All tcp packets will traverse this chain.

# Every new connection attempt should begin with

# a syn packet.  If it doesn't, it is likely a

# port scan.  This drops packets in state

# NEW that are not flagged as syn packets.





$IPT -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j LOG \

    --log-prefix "New not syn: "

$IPT -A bad_tcp_packets -p tcp ! --syn -m state --state NEW -j DROP



$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL NONE -j LOG \

    --log-prefix "Stealth scan: "

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL NONE -j DROP



$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL ALL -j LOG \

    --log-prefix "Stealth scan: "

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL ALL -j DROP



$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL FIN,URG,PSH -j LOG \

    --log-prefix "Stealth scan: "

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL FIN,URG,PSH -j DROP



$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j LOG \

    --log-prefix "Stealth scan: "

$IPT -A bad_tcp_packets -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP



$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,RST SYN,RST -j LOG \

    --log-prefix "Stealth scan: "

$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,RST SYN,RST -j DROP



$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,FIN SYN,FIN -j LOG \

    --log-prefix "Stealth scan: "

$IPT -A bad_tcp_packets -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP



# All good, so return

$IPT -A bad_tcp_packets -p tcp -j RETURN



# icmp_packets chain

#

# This chain is for inbound (from the Internet) icmp packets only.

# Type 8 (Echo Request) is not accepted by default

# Enable it if you want remote hosts to be able to reach you.

# 11 (Time Exceeded) is the only one accepted

# that would not already be covered by the established

# connection rule.  Applied to INPUT on the external interface.

# 

# See: http://www.ee.siue.edu/~rwalden/networking/icmp.html

# for more info on ICMP types.

#

# Note that the stateful settings allow replies to ICMP packets.

# These rules allow new packets of the specified types.



iptables -t filter -A INPUT -p icmp -j ACCEPT



# ICMP packets should fit in a Layer 2 frame, thus they should

# never be fragmented.  Fragmented ICMP packets are a typical sign

# of a denial of service attack.

$IPT -A icmp_packets --fragment -p ICMP -j LOG \

    --log-prefix "ICMP Fragment: "

#$IPT -A icmp_packets --fragment -p ICMP -j DROP



# Echo - uncomment to allow your system to be pinged.

# Uncomment the LOG command if you also want to log PING attempts

# 

# $IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j LOG \

#    --log-prefix "Ping detected: "

# $IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT



# By default, however, drop pings without logging. Blaster

# and other worms have infected systems blasting pings.

# Comment the line below if you want pings logged, but it

# will likely fill your logs.

#$IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j DROP



# Time Exceeded

#$IPT -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT



# Not matched, so return so it will be logged

#$IPT -A icmp_packets -p ICMP -j RETURN



# TCP & UDP

# Identify ports at:

#    http://www.chebucto.ns.ca/~rakerman/port-table.html

#    http://www.iana.org/assignments/port-numbers



# udp_inbound chain

#

# This chain describes the inbound UDP packets it will accept.

# It's applied to INPUT on the external or Internet interface.

# Note that the stateful settings allow replies.

# These rules are for new requests.

# It drops netbios packets (windows) immediately without logging.



# Drop netbios calls

# Please note that these rules do not really change the way the firewall

# treats netbios connections.  Connections from the localhost and

# internal interface (if one exists) are accepted by default.

# Responses from the Internet to requests initiated by or through

# the firewall are also accepted by default.  To get here, the

# packets would have to be part of a new request received by the

# Internet interface.  You would have to manually add rules to

# accept these.  I added these rules because some network connections,

# such as those via cable modems, tend to be filled with noise from

# unprotected Windows machines.  These rules drop those packets

# quickly and without logging them.  This prevents them from traversing

# the whole chain and keeps the log from getting cluttered with

# chatter from Windows systems.

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 137 -j DROP

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 138 -j DROP



# Network Time Protocol (NTP) Server

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 123 -j ACCEPT



# DNS Server

# Configure the server to use port 53 as the source port for requests

# Note, if you run a caching-only name server that only accepts queries

# from the private network or localhost, you can comment out this line.

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 53 -j ACCEPT



# If you don't query-source the server to port 53 and you have problems,

# uncomment this rule.  It specifically allows responses to queries

# initiated to another server from a high UDP port.  The stateful

# connection rules should handle this situation, though.

# $IPT -A udp_inbound -p UDP -s 0/0 --source-port 53 -j ACCEPT



# External DHCP Server

# Allow DHCP client request packets inbound from external network

$IPT -A udp_inbound -p UDP -s 0/0 --source-port 68 --destination-port 67 \

     -j ACCEPT



# TS3

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 9987 -j ACCEPT

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 30033 -j ACCEPT

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 10011 -j ACCEPT



# Network File System (NFS) Server

# Please note that additional services must

# be configured in order to support an NFS Server through

# the coupe-feu. Read the help in the generator or this site:

# http://www.lowth.com/LinWiz/nfs_help.html



# NFS Server - portmapper

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 111 -j ACCEPT



# NFS Server - statd

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 9400 -j ACCEPT



# NFS Server - NFS daemon

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 2049 -j ACCEPT



# NFS Server - lockd

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 9401 -j ACCEPT



# NFS Server - mountd

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 9402 -j ACCEPT



# NFS Server - quotad

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 9403 -j ACCEPT



# User specified allowed UDP protocol

$IPT -A udp_inbound -p UDP -s 0/0 --destination-port 587 -j ACCEPT





# Not matched, so return for logging

$IPT -A udp_inbound -p UDP -j RETURN



# udp_outbound chain

#

# This chain is used with a private network to prevent forwarding for

# UDP requests on specific protocols.  Applied to the FORWARD rule from

# the internal network.  Ends with an ACCEPT





# No match, so ACCEPT

$IPT -A udp_outbound -p UDP -s 0/0 -j ACCEPT



# tcp_inbound chain

#

# This chain is used to allow inbound connections to the

# system/gateway.  Use with care.  It defaults to none.

# It's applied on INPUT from the external or Internet interface.



# DNS Server - Allow TCP connections (zone transfers and large requests)

# This is disabled by default.  DNS Zone transfers occur via TCP.

# If you need to allow transfers over the net you need to uncomment this line.

# If you allow queries from the 'net, you also need to be aware that although

# DNS queries use UDP by default, a truncated UDP query can legally be

# submitted via TCP instead.  You probably will never need it, but should

# be aware of the fact.

# $IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 53 -j ACCEPT



# Web Server



# HTTP

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 80 -j ACCEPT



# HTTPS (Secure Web Server)

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 443 -j ACCEPT



# TS3

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 9987 -j ACCEPT

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 30033 -j ACCEPT

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 10011 -j ACCEPT



# FTP Server (Control)

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 21 -j ACCEPT



# FTP Client (Data Port for non-PASV transfers)

$IPT -A tcp_inbound -p TCP -s 0/0 --source-port 20 -j ACCEPT



# Passive FTP

# 

# With passive FTP, the server provides a port to the client

# and allows the client to initiate the connection rather

# than initiating the connection with the client from the data port.

# Web browsers and clients operating behind a firewall generally

# use passive ftp transfers.  A general purpose FTP server

# will need to support them.

# 

# However, by default an FTP server will select a port from the entire

# range of high ports.  It is not particularly safe to open all

# high ports.  Fortunately, that range can be restricted.  This

# firewall presumes that the range has been restricted to a specific

# selected range.  That range must also be configured in the ftp server.

# 

# Instructions for specifying the port range for the wu-ftpd server

# can be found here:

# http://www.wu-ftpd.org/man/ftpaccess.html

# (See the passive ports option.)

# 

# Instructions for the ProFTPD server can be found here:

# http://proftpd.linux.co.uk/localsite/Userguide/linked/x861.html



$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 62000:64000 -j ACCEPT



# Email Server (SMTP)

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 25 -j ACCEPT



# Email Server (POP3)

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 110 -j ACCEPT



# Email Server (IMAP4)

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 143 -j ACCEPT



# SSL Email Server (POP3)

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 995 -j ACCEPT



# SSL Email Server (IMAP4)

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 993 -j ACCEPT



# sshd

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 22 -j ACCEPT



# Network File System (NFS) Server

# Please note that additional services must

# be configured in order to support an NFS Server through

# the coupe-feu. Read the help in the generator or this site:

# http://www.lowth.com/LinWiz/nfs_help.html



# NFS Server - portmapper

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 111 -j ACCEPT



# NFS Server - statd

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 9400 -j ACCEPT



# NFS Server - NFS daemon

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 2049 -j ACCEPT



# NFS Server - lockd

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 9401 -j ACCEPT



# NFS Server - mountd

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 9402 -j ACCEPT



# NFS Server - quotad

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 9403 -j ACCEPT



# User specified allowed UDP protocol

$IPT -A tcp_inbound -p TCP -s 0/0 --destination-port 587 -j ACCEPT





# Not matched, so return so it will be logged

$IPT -A tcp_inbound -p TCP -j RETURN



# tcp_outbound chain

#

# This chain is used with a private network to prevent forwarding for

# requests on specific protocols.  Applied to the FORWARD rule from

# the internal network.  Ends with an ACCEPT





# No match, so ACCEPT

$IPT -A tcp_outbound -p TCP -s 0/0 -j ACCEPT



###############################################################################

#

# INPUT Chain

#



echo "Process INPUT chain ..."



# Allow all on localhost interface

$IPT -A INPUT -p ALL -i $LO_IFACE -j ACCEPT



# Drop bad packets

$IPT -A INPUT -p ALL -j bad_packets



# DOCSIS compliant cable modems

# Some DOCSIS compliant cable modems send IGMP multicasts to find

# connected PCs.  The multicast packets have the destination address

# 224.0.0.1.  You can accept them.  If you choose to do so,

# Uncomment the rule to ACCEPT them and comment the rule to DROP

# them  The firewall will drop them here by default to avoid

# cluttering the log.  The firewall will drop all multicasts

# to the entire subnet (224.0.0.1) by default.  To only affect

# IGMP multicasts, change '-p ALL' to '-p 2'.  Of course,

# if they aren't accepted elsewhere, it will only ensure that

# multicasts on other protocols are logged.

# Drop them without logging.

$IPT -A INPUT -p ALL -d 224.0.0.1 -j DROP

# The rule to accept the packets.

# $IPT -A INPUT -p ALL -d 224.0.0.1 -j ACCEPT





# Inbound Internet Packet Rules



# Accept Established Connections

$IPT -A INPUT -p ALL -i $INET_IFACE -m state --state ESTABLISHED,RELATED \

     -j ACCEPT



# Route the rest to the appropriate user chain

$IPT -A INPUT -p TCP -i $INET_IFACE -j tcp_inbound

$IPT -A INPUT -p UDP -i $INET_IFACE -j udp_inbound

$IPT -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets



# Drop without logging broadcasts that get this far.

# Cuts down on log clutter.

# Comment this line if testing new rules that impact

# broadcast protocols.

$IPT -A INPUT -m pkttype --pkt-type broadcast -j DROP



# Log packets that still don't match

$IPT -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \

    --log-prefix "INPUT packet died: "



###############################################################################

#

# FORWARD Chain

#



echo "Process FORWARD chain ..."



# Used if forwarding for a private network





###############################################################################

#

# OUTPUT Chain

#



echo "Process OUTPUT chain ..."



# Generally trust the coupe-feu on output



# However, invalid icmp packets need to be dropped

# to prevent a possible exploit.

$IPT -A OUTPUT -m state -p icmp --state INVALID -j DROP



# Localhost

$IPT -A OUTPUT -p ALL -s $LO_IP -j ACCEPT

$IPT -A OUTPUT -p ALL -o $LO_IFACE -j ACCEPT



# To internet

$IPT -A OUTPUT -p ALL -o $INET_IFACE -j ACCEPT



# Log packets that still don't match

$IPT -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \

    --log-prefix "OUTPUT packet died: "



###############################################################################

#

# nat table

#

###############################################################################



# The nat table is where network address translation occurs if there

# is a private network.  If the gateway is connected to the Internet

# with a static IP, snat is used.  If the gateway has a dynamic address,

# masquerade must be used instead.  There is more overhead associated

# with masquerade, so snat is better when it can be used.

# The nat table has a builtin chain, PREROUTING, for dnat and redirects.

# Another, POSTROUTING, handles snat and masquerade.



echo "Load rules for nat table ..."



###############################################################################

#

# PREROUTING chain

#





###############################################################################

#

# POSTROUTING chain

#





###############################################################################

#

# mangle table

#

###############################################################################



# The mangle table is used to alter packets.  It can alter or mangle them in

# several ways.  For the purposes of this generator, we only use its ability

# to alter the TTL in packets.  However, it can be used to set netfilter

# mark values on specific packets.  Those marks could then be used in another

# table like filter, to limit activities associated with a specific host, for

# instance.  The TOS target can be used to set the Type of Service field in

# the IP header.  Note that the TTL target might not be included in the

# distribution on your system.  If it is not and you require it, you will

# have to add it.  That may require that you build from source.



echo "Load rules for mangle table ..."