X & Gnome crashes the system with iptables

From: Jeannot Lelapin (jeannot.lelapin_at_free.fr)
Date: 08/21/03


Date: Thu, 21 Aug 2003 22:37:28 +0200

Hello,

My system is :
- Debian 3r1,
- kernel 2.4.21,
- XFree 4.1.0 (on Debian CD 3r1, I'm not connected to internet) : i use
Gnome.

I spent a lot of time to write rules for iptables to obtain a good firewall.
I join 2 files :
- the iptables rules : /etc/iptables.rules,
- the script to run it: /etc/init.d/iptables.

If i launch the firewall :
- i connect to Gnome ctrl+F7 ( it starts with the boot of the computer),
- i write login, password,
- gnome deskptop starts, displays task bar,
- nothing, i can just move the cursor of the mouse,keybord doesn't answer,
- frozen system.

If i don't launch the firewall, i havn't any trouble with Gnome.

I don't know what i can do ? ideas, advice welcome.

Sincerely yours,

Jeannot Lelapin

===========================================================
===========================================================
===========================================================
/etc/iptables.rules
===========================================================
===========================================================
===========================================================

## ============================================================
#!/bin/bash

## ===========================================================
## Load modules

IPTABLES="/sbin/iptables"
DEPMOD="/sbin/depmod"
MODPROBE="/sbin/modprobe"

# Load all required IPTables modules
# Needed to initially load modules
$DEPMOD -a
# Load appropriate modules.
$MODPROBE ip_tables
# Support for connection tracking
$MODPROBE ip_conntrack
$MODPROBE ip_conntrack_ftp

# MODIF BEGIN
$MODPROBE ip_conntrack_irc
# Adds some $IPTABLES targets like LOG, REJECT and MASQUARADE.
$MODPROBE ipt_LOG
$MODPROBE ipt_REJECT
$MODPROBE ipt_MASQUERADE
# Support for owner matching
$MODPROBE ipt_owner
# MODIF END

## ===========================================================
## Reset all configurations
#
# These lines are here in case rules are already in place and the script
is ever rerun on the fly.
# We want to :
# - remove all rules,
# - remove pre-exisiting user defined chains,
# - zero the counters.
# before we implement new rules.

$IPTABLES -F
$IPTABLES -X
$IPTABLES -Z

## ===========================================================
## Default Policy
#
# Set up a default DROP policy for the built-in chains.
# If we modify and re-run the script mid-session then (because we have a
default DROP
# policy), what happens is that there is a small time period when
packets are denied until
# the new rules are back in place. There is no period, however small,
when packets we
# don't want are allowed.
$IPTABLES -P INPUT DROP
$IPTABLES -P FORWARD DROP
$IPTABLES -P OUTPUT DROP

## ===========================================================
## Some definitions:

# Le DNS primaire du fournisseur d'accès Free
NAMESERVER_1="212.27.32.5"
# Le DNS secondaire du fournisseur d'accès Free
NAMESERVER_2="212.27.32.6"

# Note : si je mets des FQDN, iptables essaye de les résoudre. Comme le
réseau n'est pas encore branché, ca tombe à l'eau.
# Il faudra peut etre prévoir le fait rejouer les règles avec des FDQN
une fois la connexion ADSL ou PPP établie.

# Le serveur de courrier POP du fournisseur d'accès Free
# Le FQDN : pop.free.fr : 213.228.0.14, 213.228.0.141, 213.228.0.142,
213.228.0.165 213.228.0.12
INCOMINGMAILSERVER_1="213.228.0.14"
# Le serveur de courrier POP du fournisseur d'accès Club-Internet
# Le FQDN : mail.club-internet.fr : 195.36.166.10, 195.36.162.10
INCOMINGMAILSERVER_2="195.36.166.10"
# Le serveur de courrier SMTP du fournisseur d'accès Free
# Le FQDN : smtp.free.fr : 213.228.0.44, 213.228.0.62, 213.228.0.169,
213.228.0.176
OUTGOINGMAILSERVER="213.228.0.44"

# Les serveurs de temps
# Le FQDN : ntp.uvsq.fr : 193.51.24.1
TIMESERVER_1="193.51.24.1"
# Le FQDN : delphi.phys.univ-tours.fr : 193.52.212.3
TIMESERVER_2="193.52.212.3"
# Le FQDN : ntp0.oleane.net : 194.2.0.28
TIMESERVER_3="194.2.0.28"
# Le FQDN : ntp1.oleane.net : 94.2.0.58
TIMESERVER_4="94.2.0.58"
# Le FQDN : ntp.via.ecp.fr : 138.195.130.71
TIMESERVER_5="138.195.130.71"
# Le FQDN : ntp.chronos.org : 129.186.121.29
TIMESERVER_6="129.186.121.29"

LOOPBACK="127.0.0.0/8"
BROADCAST="x.x.x.255"
CLASS_A="10.0.0.0/8"
CLASS_B="172.16.0.0/12"
CLASS_C="192.168.0.0/16"
CLASS_D_MULTICAST="224.0.0.0/4"
CLASS_E_RESERVED_NET="240.0.0.0/5"
P_PORTS="0:1023"
UP_PORTS="1024:65535"
TR_SRC_PORTS="32769:65535"
TR_DEST_PORTS="33434:33523"

## ============================================================
## Kernel flags
#
# To dynamically change kernel parameters and variables on the fly you need
# CONFIG_SYSCTL defined in your kernel. I would advise the following:

# If you get your IP address dynamically from SLIP, PPP, or DHCP, enable
this
# option. This enables dynamic-ip address hacking in IP MASQ, making the
connection
# with Diald and similar programs much easier.
# MODIF BEGIN
echo "1" > /proc/sys/net/ipv4/ip_dynaddr
# MODIF END

# Disable response to ping.
/bin/echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_all

# Disable response to broadcasts.
# You don't want yourself becoming a Smurf amplifier.
/bin/echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

# Don't accept source routed packets. Attackers can use source routing
to generate
# traffic pretending to be from inside your network, but which is routed
back along
# the path from which it came, namely outside, so attackers can
compromise your
# network. Source routing is rarely used for legitimate purposes.
/bin/echo "0" > /proc/sys/net/ipv4/conf/all/accept_source_route

# Disable ICMP redirect acceptance. ICMP redirects can be used to alter
your routing
# tables, possibly to a bad end.
/bin/echo "0" > /proc/sys/net/ipv4/conf/all/accept_redirects

# Enable bad error message protection.
/bin/echo "1" > /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses

# Turn on reverse path filtering. This helps make sure that packets use
# legitimate source addresses, by automatically rejecting incoming packets
# if the routing table entry for their source address doesn't match the
network
# interface they're arriving on. This has security advantages because it
prevents
# so-called IP spoofing, however it can pose problems if you use
asymmetric routing
# (packets from you to a host take a different path than packets from
that host to you)
# or if you operate a non-routing host which has several IP addresses on
different
# interfaces. (Note - If you turn on IP forwarding, you will also get this).
for interface in /proc/sys/net/ipv4/conf/*/rp_filter; do
    /bin/echo "1" > ${interface}
done

# Log spoofed packets, source routed packets, redirect packets.
/bin/echo "1" > /proc/sys/net/ipv4/conf/all/log_martians

# Make sure that IP forwarding is turned off. We only want this for a
multi-homed host.
/bin/echo "0" > /proc/sys/net/ipv4/ip_forward

# Note: With connection tracking, all fragments are reassembled before being
# passed to the packet-filtering code so there is no ip_always_defrag
switch as there
# was in the 2.2 kernel.

## ============================================================
# RULES

## SYN-FLOODING PROTECTION
# This rule maximises the rate of incoming connections. In order to do
this we divert tcp
# packets with the SYN bit set off to a user-defined chain. Up to
limit-burst connections
# can arrive in 1/limit seconds ..... in this case 4 connections in one
second. After this, one
# of the burst is regained every second and connections are allowed
again. The default limit
# is 3/hour. The default limit burst is 5.
#
$IPTABLES -N syn-flood
$IPTABLES -A INPUT -p tcp --syn -j syn-flood
$IPTABLES -A syn-flood -m limit --limit 1/s --limit-burst 4 -j RETURN
$IPTABLES -A syn-flood -j DROP

## FRAGMENTS
# I have to say that fragments scare me more than anything.
# Sending lots of non-first fragments was what allowed Jolt2 to
effectively "drown"
# Firewall-1. Fragments can be overlapped, and the subsequent
interpretation of such
# fragments is very OS-dependent (see this paper for details).
# I am not going to trust any fragments.
# Log fragments just to see if we get any, and deny them too.
$IPTABLES -A INPUT -f -j LOG --log-prefix "IPTABLES FRAGMENTS: "
$IPTABLES -A INPUT -f -j DROP

## SPOOFING
# Most of this anti-spoofing stuff is theoretically not really necessary
with the flags we
# have set in the kernel above ........... but you never know there
isn't a bug somewhere in
# your IP stack.
#
# Refuse spoofed packets pretending to be from your IP address.
# ( CETTE REGLE SERA MISE EN OEUVRE LORSQUE JE RECUPERERAI L'ADRESSE IP
DES INTERFACES CONCERNEES )
#$IPTABLES -A INPUT -s $IPADDR -j DROP
# Refuse packets claiming to be from a Class A private network.
$IPTABLES -A INPUT -s $CLASS_A -j DROP
# Refuse packets claiming to be from a Class B private network.
$IPTABLES -A INPUT -s $CLASS_B -j DROP
# Refuse packets claiming to be from a Class C private network.
$IPTABLES -A INPUT -s $CLASS_C -j DROP
# Refuse Class D multicast addresses. Multicast is illegal as a source
address.
$IPTABLES -A INPUT -s $CLASS_D_MULTICAST -j DROP
# Refuse Class E reserved IP addresses.
$IPTABLES -A INPUT -s $CLASS_E_RESERVED_NET -j DROP
# Refuse packets claiming to be to the loopback interface.
# Refusing packets claiming to be to the loopback interface protects against
# source quench, whereby a machine can be told to slow itself down by an
icmp source
# quench to the loopback.
$IPTABLES -A INPUT -d $LOOPBACK -j DROP
# Refuse broadcast address packets.
# ( CETTE REGLE SERA MISE EN OEUVRE LORSQUE JE RECUPERERAI L'ADRESSE DES
SOUS RESEAUX DES INTERFACES CONCERNEES )
#$IPTABLES -A INPUT -d $BROADCAST -j DROP

## TELNET
# Allow telnet outbound.
#$IPTABLES -A INPUT -p tcp --sport 23 -m state --state ESTABLISHED -j
ACCEPT
#$IPTABLES -A OUTPUT -p tcp --dport 23 -m state --state NEW,ESTABLISHED
-j ACCEPT

## FTP
# Allow ftp outbound.
#$IPTABLES -A INPUT -p tcp --sport 21 -m state --state ESTABLISHED -j
ACCEPT
#$IPTABLES -A OUTPUT -p tcp --dport 21 -m state --state NEW,ESTABLISHED
-j ACCEPT
# Now for the connection tracking part of ftp. This is discussed more
completely in my section
# on connection tracking to be found here.
# 1) Active ftp.
# This involves a connection INbound from port 20 on the remote machine,
to a local port
# passed over the ftp channel via a PORT command. The ip_conntrack_ftp
module recognizes
# the connection as RELATED to the original outgoing connection to port
21 so we don't
# need NEW as a state match.
#$IPTABLES -A INPUT -p tcp --sport 20 -m state --state
ESTABLISHED,RELATED -j ACCEPT
#$IPTABLES -A OUTPUT -p tcp --dport 20 -m state --state ESTABLISHED -j
ACCEPT
# 2) Passive ftp.
# This involves a connection outbound from a port >1023 on the local
machine, to a port >1023
# on the remote machine previously passed over the ftp channel via a
PORT command. The
# ip_conntrack_ftp module recognizes the connection as RELATED to the
original outgoing
# connection to port 21 so we don't need NEW as a state match.
#$IPTABLES -A INPUT -p tcp --sport $UP_PORTS --dport $UP_PORTS -m
state --state ESTABLISHED -j ACCEPT
#$IPTABLES -A OUTPUT -p tcp --sport $UP_PORTS --dport $UP_PORTS -m
state --state ESTABLISHED,RELATED -j ACCEPT

## Make sure NEW tcp connections are SYN packets
$IPTABLES -A INPUT -p tcp ! --syn -m state --state NEW -j DROP

## LOOPBACK
# Allow unlimited traffic on the loopback interface.
$IPTABLES -A INPUT -i lo -j ACCEPT
$IPTABLES -A OUTPUT -o lo -j ACCEPT

## DNS
# NOTE: DNS uses tcp for zone transfers, for transfers greater than 512
bytes (possible, but unusual), and on certain
# platforms like AIX (I am told), so you might have to add a copy of
this rule for tcp if you need it
# Allow UDP packets in for DNS client from nameservers.
$IPTABLES -A INPUT -p udp -s $NAMESERVER_1 --sport 53 -m state --state
ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p udp -s $NAMESERVER_2 --sport 53 -m state --state
ESTABLISHED -j ACCEPT
# Allow UDP packets to DNS servers from client.
$IPTABLES -A OUTPUT -p udp -d $NAMESERVER_1 --dport 53 -m state --state
NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p udp -d $NAMESERVER_2 --dport 53 -m state --state
NEW,ESTABLISHED -j ACCEPT

## WWW
# Allow www outbound to 80.
$IPTABLES -A INPUT -p tcp --sport 80 -m state --state ESTABLISHED -j
ACCEPT
$IPTABLES -A OUTPUT -p tcp --dport 80 -m state --state NEW,ESTABLISHED
-j ACCEPT

# Allow www outbound to 443. JE METS LE SERVEUR SSH SUR CE PORT
#$IPTABLES -A INPUT -p tcp --sport 443 -m state --state ESTABLISHED -j
ACCEPT
#$IPTABLES -A OUTPUT -p tcp --dport 443 -m state --state
NEW,ESTABLISHED -j ACCEPT

## SSH
# Allow ssh outbound.
$IPTABLES -A INPUT -p tcp --sport 443 -m state --state NEW,ESTABLISHED
-j ACCEPT
$IPTABLES -A OUTPUT -p tcp --dport 443 -m state --state NEW,ESTABLISHED
-j ACCEPT

## SMTP
# Allow smtp outbound.
$IPTABLES -A INPUT -p tcp -s $OUTGOINGMAILSERVER --sport 25 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p tcp -d $OUTGOINGMAILSERVER --dport 25 -m state
--state NEW,ESTABLISHED -j ACCEPT

## POP
# Allow pop outbound.
$IPTABLES -A INPUT -p tcp -s $INCOMINGMAILSERVER_1 --sport 110 -m
state --state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p tcp -s $INCOMINGMAILSERVER_2 --sport 110 -m
state --state ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p tcp -d $INCOMINGMAILSERVER_1 --dport 110 -m
state --state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p tcp -d $INCOMINGMAILSERVER_2 --dport 110 -m
state --state NEW,ESTABLISHED -j ACCEPT

## AUTH server
# Reject ident probes with a tcp reset.
# I need to do this for a broken mailhost that won't accept my mail if I
just drop its ident probe.
$IPTABLES -A INPUT -p tcp --dport 113 -j REJECT --reject-with tcp-reset

## TRACEROUTE
# Outgoing traceroute anywhere.
# The reply to a traceroute is an icmp time-exceeded which is dealt with
by the next rule.
$IPTABLES -A OUTPUT -p udp --sport $TR_SRC_PORTS --dport $TR_DEST_PORTS
-m state --state NEW -j ACCEPT

## NTP
# Allow ntp outbound.
$IPTABLES -A INPUT -p tcp -s $TIMESERVER_1 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p udp -s $TIMESERVER_1 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p tcp -s $TIMESERVER_2 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p udp -s $TIMESERVER_2 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p tcp -s $TIMESERVER_3 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p udp -s $TIMESERVER_3 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p tcp -s $TIMESERVER_4 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p udp -s $TIMESERVER_4 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p tcp -s $TIMESERVER_5 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p udp -s $TIMESERVER_5 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p tcp -s $TIMESERVER_6 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A INPUT -p udp -s $TIMESERVER_6 --sport 123 -m state
--state ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_1 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p udp -d $TIMESERVER_1 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_2 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p udp -d $TIMESERVER_2 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_3 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p udp -d $TIMESERVER_3 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_4 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p udp -d $TIMESERVER_4 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_5 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p udp -d $TIMESERVER_5 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p tcp -d $TIMESERVER_6 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT
$IPTABLES -A OUTPUT -p udp -d $TIMESERVER_6 --dport 123 -m state
--state NEW,ESTABLISHED -j ACCEPT

# ICMP
# We accept icmp in if it is "related" to other connections (e.g a time
exceeded (11)
# from a traceroute) or it is part of an "established" connection (e.g.
an echo reply (0)
# from an echo-request (8)).
$IPTABLES -A INPUT -p icmp -m state --state ESTABLISHED,RELATED -j ACCEPT
# We always allow icmp out.
$IPTABLES -A OUTPUT -p icmp -m state --state NEW,ESTABLISHED,RELATED -j
ACCEPT

## LOGGING
# You don't have to split up your logging like I do below, but I prefer
to do it this way
# because I can then grep for things in the logs more easily. One thing
you probably want
# to do is rate-limit the logging. I didn't do that here because it is
probably best not too
# when you first set things up ................. you actually really
want to see everything going to
# the logs to work out what isn't working and why. You cam implement
logging with
# "-m limit --limit 6/h --limit-burst 5" (or similar) before the -j LOG
in each case.
#
# Any udp not already allowed is logged and then dropped.
$IPTABLES -A INPUT -p udp -j LOG --log-prefix "IPTABLES UDP-IN: "
$IPTABLES -A INPUT -p udp -j DROP
$IPTABLES -A OUTPUT -p udp -j LOG --log-prefix "IPTABLES UDP-OUT: "
$IPTABLES -A OUTPUT -p udp -j DROP
# Any icmp not already allowed is logged and then dropped.
$IPTABLES -A INPUT -p icmp -j LOG --log-prefix "IPTABLES ICMP-IN: "
$IPTABLES -A INPUT -p icmp -j DROP
$IPTABLES -A OUTPUT -p icmp -j LOG --log-prefix "IPTABLES ICMP-OUT: "
$IPTABLES -A OUTPUT -p icmp -j DROP
# Any tcp not already allowed is logged and then dropped.
$IPTABLES -A INPUT -p tcp -j LOG --log-prefix "IPTABLES TCP-IN: "
$IPTABLES -A INPUT -p tcp -j DROP
$IPTABLES -A OUTPUT -p tcp -j LOG --log-prefix "IPTABLES TCP-OUT: "
$IPTABLES -A OUTPUT -p tcp -j DROP
# Anything else not already allowed is logged and then dropped.
# It will be dropped by the default policy anyway ........ but let's be
paranoid.
$IPTABLES -A INPUT -j LOG --log-prefix "IPTABLES PROTOCOL-X-IN: "
$IPTABLES -A INPUT -j DROP
$IPTABLES -A OUTPUT -j LOG --log-prefix "IPTABLES PROTOCOL-X-OUT: "
$IPTABLES -A OUTPUT -j DROP

# THE END
# ==================================================================

===========================================================
===========================================================
===========================================================
/etc/init.d/iptables
===========================================================
===========================================================
===========================================================

#!/bin/sh
#
# chkconfig: 2345 08 92
#

IPTABLES_CONFIG=/etc/iptables.rules

# check we have the iptables executable
if [ ! -x /sbin/iptables ]; then
   exit 0
fi

# check we have the right kernel version
KERNELMAJ=`uname -r | sed -e 's,\..*,,'`
KERNELMIN=`uname -r | sed -e 's,[^\.]*\.,,' -e 's,\..*,,'`
if [ "$KERNELMAJ" -lt 2 ] ; then
   exit 0
fi
if [ "$KERNELMAJ" -eq 2 -a "$KERNELMIN" -lt 3 ] ; then
   exit 0
fi

if /sbin/lsmod 2>/dev/null |grep -q ipchains ; then
   # Don't do both
   exit 0
fi

start() {
   # don't do squat if we don't have the script
   if [ -f $IPTABLES_CONFIG ]; then
     echo "Applying iptables firewall rules:"
     /etc/iptables.rules
     touch /var/lock/subsys/iptables
   fi
}

stop() {
   echo "Flushing all chains:"
   iptables -F
   echo "Removing user defined chains:"
   iptables -X
   echo "Resetting built-in chains to the default ACCEPT policy:"
   iptables -P INPUT ACCEPT && iptables -P FORWARD ACCEPT && iptables -P
OUTPUT ACCEPT &&
   # IL FAUT RECUPERER LE RESULTAT DE L'EXECUTION ET FAIRE LES ECHOS EN
CONSEQUENCE
   # success "Resetting built-in chains to the default ACCEPT policy" ||
   # failure "Resetting built-in chains to the default ACCEPT policy"
   rm -f /var/lock/subsys/iptables
}

case "$1" in
   start)
     start
   ;;

   stop)
     stop
   ;;

   restart)
     # "restart" is really just "start" as this isn't a daemon,
     # and "start" clears any pre-defined rules anyway.
     # This is really only here to make those who expect it happy
     start
   ;;

   status)
     iptables --list
   ;;

   panic)
     echo "Changing target policies to DROP: "
     iptables -P INPUT DROP && iptables -P FORWARD DROP && iptables -P
OUTPUT DROP
     # IL FAUT RECUPERER LE RESULTAT DE L'EXECUTION ET FAIRE LES ECHOS
EN CONSEQUENCE
     # success "Changing target policies to DROP" || \
     # failure "Changing target policies to DROP"
     echo
     echo "Flushing all chains:"
     iptables -F INPUT && iptables -F FORWARD && iptables -F OUTPUT
     echo
     echo "Removing user defined chains:"
     iptables -X
   ;;

   *)
     echo "Usage: $0 {start|stop|restart|status|panic}"
     exit 1
esac

exit 0



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