Iptables Tutorial 1.1.19

Andreasson Oskar

# from; if not, write to the Free Software Foundation, Inc., 59 Temple

# Place, Suite 330, Boston, MA 02111-1307 USA

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# 1. Configuration options.

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# 1.1 Internet Configuration.

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INET_IP="194.236.50.152"

HTTP_IP="194.236.50.153"

DNS_IP="194.236.50.154"

INET_IFACE="eth0"

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# 1.1.1 DHCP

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# 1.1.2 PPPoE

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# 1.2 Local Area Network configuration.

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# your LAN's IP range and localhost IP. /24 means to only use the first 24

# bits of the 32 bit IP address. the same as netmask 255.255.255.0

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LAN_IP="192.168.0.1"

LAN_IFACE="eth1"

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# 1.3 DMZ Configuration.

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DMZ_HTTP_IP="192.168.1.2"

DMZ_DNS_IP="192.168.1.3"

DMZ_IP="192.168.1.1"

DMZ_IFACE="eth2"

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# 1.4 Localhost Configuration.

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LO_IFACE="lo"

LO_IP="127.0.0.1"

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# 1.5 IPTables Configuration.

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IPTABLES="/usr/sbin/iptables"

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# 1.6 Other Configuration.

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

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# 2. Module loading.

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# Needed to initially load modules

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/sbin/depmod -a

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# 2.1 Required modules

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/sbin/modprobe ip_tables

/sbin/modprobe ip_conntrack

/sbin/modprobe iptable_filter

/sbin/modprobe iptable_mangle

/sbin/modprobe iptable_nat

/sbin/modprobe ipt_LOG

/sbin/modprobe ipt_limit

/sbin/modprobe ipt_state

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# 2.2 Non-Required modules

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#/sbin/modprobe ipt_owner

#/sbin/modprobe ipt_REJECT

#/sbin/modprobe ipt_MASQUERADE

#/sbin/modprobe ip_conntrack_ftp

#/sbin/modprobe ip_conntrack_irc

#/sbin/modprobe ip_nat_ftp

#/sbin/modprobe ip_nat_irc

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

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# 3. /proc set up.

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# 3.1 Required proc configuration

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

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# 3.2 Non-Required proc configuration

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

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

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

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

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# 4. rules set up.

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# 4.1 Filter table

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# 4.1.1 Set policies

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$IPTABLES -P INPUT DROP

$IPTABLES -P OUTPUT DROP

$IPTABLES -P FORWARD DROP

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# 4.1.2 Create userspecified chains

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# Create chain for bad tcp packets

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$IPTABLES -N bad_tcp_packets

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

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$IPTABLES -N allowed

$IPTABLES -N icmp_packets

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# 4.1.3 Create content in userspecified chains

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# bad_tcp_packets chain

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$IPTABLES -A bad_tcp_packets -p tcp –tcp-flags SYN,ACK SYN,ACK \

–m state –state NEW -j REJECT –reject-with tcp-reset

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

–log-prefix

«New not syn:»

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

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# allowed chain

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$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

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# ICMP rules

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# Changed rules totally

$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

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# 4.1.4 INPUT chain

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# Bad TCP packets we don't want

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$IPTABLES -A INPUT -p tcp -j bad_tcp_packets

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# Packets from the Internet to this box

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

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# Packets from LAN, DMZ or LOCALHOST

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# From DMZ Interface to DMZ firewall IP

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$IPTABLES -A INPUT -p ALL -i $DMZ_IFACE -d $DMZ_IP -j ACCEPT