Masquerading problem

[Spiros Bolis]

On Fri, 20 Jul 2001, Nikos Kanellopoulos wrote:

> > H lysh...
> >
> > http://www.boingworld.com/workshops/linux/iptables-tutorial/rc.firewall.txt
> >
> > Emena moy doylepse (mallon kala ?..)
> > An kai prospathisa na katalabw th diafora den ebgala akrh..
> >
> > kapoios poy borei na diakrinei kamia trypara sto parapanw script ?
> >
> > Kalh tyxh Niko,
> >
> >
> > Spiros D. Bolis
>
> Spyro, epeidh oute ping den mporw na kanw ton pio panw server, mporeis na mou
> steileis to arxeio afto?
> H'  grapse tous swstous kanones.
Den 3erw an einai swstoi alla aytoi einai ;-)
Exei arketa sxolia opote...
{
Me thn eykairia... an thelhsw na balw ena transparent proxy..
arkei na thesw mia grammh opws ayth xwris na alla3w kati allo ?

iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT
--to-port 3128
}


#!/bin/sh
#
# rc.firewall - Initial SIMPLE IP Firewall test script for 2.4.x
#
# Author: Oskar Andreasson <blueflux at koffein.net>
# (c) of BoingWorld.com, use at your own risk, do whatever you please with
# it as long as you don't distribute this with due credits to
# BoingWorld.com
#

###########
# Configuration options, these will speed you up getting this script to
# work with your own setup.

#
# your LAN's IP range and localhost IP. /24 means to only use the first 24
# bits of the 32 bit IP adress. the same as netmask 255.255.255.0
#
# STATIC_IP is used by me to allow myself to do anything to myself, might
# be a security risc but sometimes I want this. If you don't have a static
# IP, I suggest not using this option at all for now but it's still
# enabled per default and will add some really nifty security bugs for all
# those who skips reading the documentation=)

LAN_IP_RANGE="192.168.100.0/24"
LAN_IP="192.168.100.100/32"
LAN_BCAST_ADRESS="192.168.100.255/32"
LOCALHOST_IP="127.0.0.1/32"
STATIC_IP="195.134.76.150/32"
INET_IFACE="eth0"
LAN_IFACE="eth1"
IPTABLES="/sbin/iptables"

#########
# Load all required IPTables modules
#

#
# Needed to initially load modules
#
/sbin/depmod -a

#
# Adds some iptables targets like LOG, REJECT and MASQUARADE.
#
/sbin/modprobe ipt_LOG
#/sbin/modprobe ipt_REJECT
#/sbin/modprobe ipt_MASQUERADE

#
# Support for owner matching
#
#/sbin/modprobe ipt_owner

#
# Support for connection tracking of FTP and IRC.
#
#/sbin/modprobe ip_conntrack_ftp
#/sbin/modprobe ip_conntrack_irc


#CRITICAL:  Enable IP forwarding since it is disabled by default.
#
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
#       option.  This enables dynamic-ip address hacking in IP MASQ, making the connection
#       with Diald and similar programs much easier.
#
#echo "1" > /proc/sys/net/ipv4/ip_dynaddr

# Enable simple IP FORWARDing and Masquerading
#
#  NOTE:  The following is an example for an internal LAN, where the lan
#         runs on eth1, and the Internet is on eth0.
#
#         Please change the network devices to match your own configuration.
#

$IPTABLES -t nat -A POSTROUTING -o $INET_IFACE -j MASQUERADE
$IPTABLES -A FORWARD -i $LAN_IFACE -j ACCEPT
$IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A FORWARD -m limit --limit 3/minute --limit-burst 3 -j LOG --log-level DEBUG --log-prefix "IPT FORWARD packet died: "

#
# set default policies for the INPUT, FORWARD and OUTPUT chains
#

$IPTABLES -P INPUT DROP
$IPTABLES -P OUTPUT DROP
$IPTABLES -P FORWARD DROP

#
# Create separate chains for ICMP, TCP and UDP to traverse
#

$IPTABLES -N icmp_packets
$IPTABLES -N tcp_packets
$IPTABLES -N udpincoming_packets

#
# the allowed chain for TCP connections
#
# This chain will be utilised if someone tries to connect to an allowed
# port from the internet. If they are opening the connection, or if it's
# already established we ACCEPT the packages, if not we fuck them. This is
# where the state matching is performed also, we allow ESTABLISHED and
# RELATED packets.

$IPTABLES -N allowed
$IPTABLES -A allowed -p TCP --syn -j ACCEPT
$IPTABLES -A allowed -p TCP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A allowed -p TCP -j DROP

#
# ICMP rules
#

$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 0 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 3 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 5 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 8 -j ACCEPT
$IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT

#
# TCP rules
#

$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 21 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 22 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 23 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 80 -j allowed
$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 3128 -j allowed
#$IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 113 -j allowed

#
# UDP ports
#

$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT
#$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 123 -j ACCEPT
#$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 2074 -j ACCEPT
#$IPTABLES -A udpincoming_packets -p UDP -s 0/0 --source-port 4000 -j ACCEPT

#
# PREROUTING chain.
#
# Do some checks for obviously spoofed IP's
#

$IPTABLES -t nat -A PREROUTING -i $INET_IFACE -s 192.168.0.0/16 -j DROP
$IPTABLES -t nat -A PREROUTING -i $INET_IFACE -s 10.0.0.0/8 -j DROP
$IPTABLES -t nat -A PREROUTING -i $INET_IFACE -s 172.16.0.0/12 -j DROP


#
# INPUT chain
#
# establish the basic INPUT chain and filter the packets onto the correct
# chains.
#


$IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets
$IPTABLES -A INPUT -p TCP -i $INET_IFACE -j tcp_packets
$IPTABLES -A INPUT -p UDP -i $INET_IFACE -j udpincoming_packets

$IPTABLES -A INPUT -p ALL -i $LAN_IFACE -d $LAN_BCAST_ADRESS -j ACCEPT
$IPTABLES -A INPUT -p ALL -d $LOCALHOST_IP -j ACCEPT
$IPTABLES -A INPUT -p ALL -d $LAN_IP -j ACCEPT
$IPTABLES -A INPUT -p ALL -d $STATIC_IP -m state --state ESTABLISHED,RELATED -j ACCEPT
$IPTABLES -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG --log-level DEBUG --log-prefix "IPT INPUT packet died: "

#
# OUTPUT chain
#
# establish the basic OUTPUT chain and filter them onto the correct chain
#

$IPTABLES -A OUTPUT -p ALL -s $LOCALHOST_IP -j ACCEPT
$IPTABLES -A OUTPUT -p ALL -s $LAN_IP -j ACCEPT
$IPTABLES -A OUTPUT -p ALL -s $STATIC_IP -j ACCEPT
$IPTABLES -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG --log-level DEBUG --log-prefix "IPT OUTPUT packet died: "



Spiros D. Bolis