Re: problem with dmz firewall script - cant connect to inet via plan

From: steve harris (steveharris1@REMOVECAPShotmail.com)
Date: 12/10/02


From: steve harris <steveharris1@REMOVECAPShotmail.com>
Date: Mon, 09 Dec 2002 19:43:47 -0600

bob wrote:

> Hi,
> can anyone tell me why my firewall script is not working correctly.
> Everything is fine but I can not access the internet from my private
> lan. I have a dmz and seperate trusted private lan multihomed on the
> firewall box connected to the internet via a dsl connection. The
> external interface card is aliased with real ip addresses and dnat'ed
> through to the dmz. The box runs linux redhat 7.2 and I am using
> iptables (userspace) as my packet filter. I have looked at this for a
> while but am now at a loss for further testing. The strange thing is
> that windows clients on the private lan have internet access ok but
> when I try to connect a linux client to the internet via the private
> lan it does not work. Does the static route table have to be set up as
> normal on the private lan box ? i.e. add host, networks and default
> gateway - if so should I be able to ping the dsl router via the
> firewall ?
>
>
> I have included my firewall script :
>
> #!/bin/sh
> # rc.DMZ.firewall - DMZ IP Firewall script for Linux 2.4.x and
> iptables
> # 1. Configuration options.
>
> ######### Internet Configuration.
> INET_IP="81.2.94.210"
> HTTP_IP="81.2.94.211"
> DNS_IP="81.2.94.212"
> INET_IFACE="eth0"
>
>
> ######## Local Area Network configuration.
> LAN_IP="192.168.0.2"
> LAN_IP_RANGE="192.168.0.0/16"
> LAN_BROADCAST_ADDRESS="192.168.0.255"
> LAN_IFACE="eth1"
>
> ######## Display status information
> echo "---------------------------------------------------------"
> echo "HTTP IP: $HTTP_IP"
> echo "DNS IP: $DNS_IP"
> echo "External Network Device: $INET_IP"
> echo "External IP: $INET_IP"
> echo "Local Network Address: $LAN_IP"
> echo "---------------------------------------------------------"
>
> ALLOW_ICMP="0 3 4 5 8 11 12"
>
> ######## DMZ Configuration.
> DMZ_HTTP_IP="192.168.1.3"
> DMZ_DNS_IP="192.168.1.4"
> DMZ_IP="192.168.1.2"
> DMZ_IP_RANGE="192.168.1.0/16"
> DMZ_IFACE="eth2"
>
> ######## Localhost Configuration.
> LO_IFACE="lo"
> LO_IP="127.0.0.1"
>
>
> # IPTables Configuration.
> IPTABLES="/sbin/iptables"
>
> # Other Configuration.
>
> # Module loading.
> # Needed to initially load modules
> /sbin/depmod -a
> # 2.1 Required modules
> /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
>
> # 2.2 Non-Required modules
> #/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
>
> # 3. /proc set up.
> # 3.1 Required proc configuration
>
> echo "1" > /proc/sys/net/ipv4/ip_forward
>
> # 3.2 Non-Required proc configuration
> #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
>
>
> # Rules set up.
> ###### FILTER TABLE ############
>
> # Set policies
> $IPTABLES -P INPUT DROP
> $IPTABLES -P OUTPUT DROP
> $IPTABLES -P FORWARD DROP
>
> # Create userspecified chains
>
> # Create chain for bad tcp packets
> $IPTABLES -N bad_tcp_packets
>
> # Create separate chains for ICMP, TCP and UDP to traverse
> $IPTABLES -N allowed
> $IPTABLES -N icmp_packets
> $IPTABLES -N tcp_packets
> $IPTABLES -N udpincoming_packets
>
> # Create content in userspecified chains
>
> # bad_tcp_packets chain
> $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
>
> # allowed chain
> $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
> # Changed rules totally
> $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 8 -j ACCEPT
> $IPTABLES -A icmp_packets -p ICMP -s 0/0 --icmp-type 11 -j ACCEPT
>
>
> ######## INPUT chain ############
>
> # Bad TCP packets we don't want
> $IPTABLES -A INPUT -p tcp -j bad_tcp_packets
>
> # Packets from the Internet to this box
> $IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets
>
> # Packets from LAN, DMZ or LOCALHOST
>
> # From DMZ Interface to DMZ firewall IP
> $IPTABLES -A INPUT -p ALL -i $DMZ_IFACE -d $DMZ_IP -j ACCEPT
>
> # From LAN Interface to LAN firewall IP
> $IPTABLES -A INPUT -p ALL -i $LAN_IFACE -d $LAN_IP_RANGE -j ACCEPT
> $IPTABLES -A INPUT -p ALL -i $LAN_IFACE -d $LAN_BROADCAST_ADDRESS -j
> ACCEPT
>
> # From Localhost interface to Localhost IP's
> $IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $LO_IP -j ACCEPT
> $IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $LAN_IP_RANGE -j ACCEPT
> $IPTABLES -A INPUT -p ALL -i $LO_IFACE -s $INET_IP -j ACCEPT
>
> # Special rule for DHCP requests from LAN, which are not caught
> properly
> # otherwise.
> $IPTABLES -A INPUT -p UDP -i $LAN_IFACE --dport 67 --sport 68 -j
> ACCEPT
>
> # All established and related packets incoming from the internet to
> the
> # firewall
> #
>
> $IPTABLES -A INPUT -p ALL -d $INET_IP -m state --state
> ESTABLISHED,RELATED \
> -j ACCEPT
>
> # Log weird packets that don't match the above.
> $IPTABLES -A INPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \
> --log-level DEBUG --log-prefix "IPT INPUT packet died: "
>
>
> ######## FORWARD chain ###########
>
> # Bad TCP packets we don't want
> $IPTABLES -A FORWARD -p tcp -j bad_tcp_packets
>
> ## DMZ section
> ## General rules
> $IPTABLES -A FORWARD -i $DMZ_IFACE -o $INET_IFACE -j ACCEPT
> $IPTABLES -A FORWARD -i $INET_IFACE -o $DMZ_IFACE -m state \
> --state ESTABLISHED,RELATED -j ACCEPT
> $IPTABLES -A FORWARD -i $LAN_IFACE -o $DMZ_IFACE -j ACCEPT
> $IPTABLES -A FORWARD -i $DMZ_IFACE -o $LAN_IFACE -j ACCEPT
> #set up allow traffic from lan to inet and back again
> $IPTABLES -A FORWARD -i $LAN_IFACE -o $INET_IFACE -j ACCEPT
> $IPTABLES -A FORWARD -i $INET_IFACE -o $LAN_IFACE -m state \
> --state ESTABLISHED,RELATED -j ACCEPT
>
>
> ## HTTP server
> $IPTABLES -A FORWARD -p TCP -i $INET_IFACE -o $DMZ_IFACE -d
> $DMZ_HTTP_IP \
> --dport 80 -j allowed
> $IPTABLES -A FORWARD -p ICMP -i $INET_IFACE -o $DMZ_IFACE -d
> $DMZ_HTTP_IP \
> -j icmp_packets
> $IPTABLES -A FORWARD -p TCP -i $INET_IFACE -o $DMZ_IFACE -d
> $DMZ_HTTP_IP \
> -s 0/0 --dport 22 -j allowed
>
> ## DNS server
> $IPTABLES -A FORWARD -p TCP -i $INET_IFACE -o $DMZ_IFACE -d
> $DMZ_DNS_IP \
> --dport 53 -j allowed
> $IPTABLES -A FORWARD -p UDP -i $INET_IFACE -o $DMZ_IFACE -d
> $DMZ_DNS_IP \
> --dport 53 -j ACCEPT
> $IPTABLES -A FORWARD -p ICMP -i $INET_IFACE -o $DMZ_IFACE -d
> $DMZ_DNS_IP \
> -j icmp_packets
>
> ## LAN section
> $IPTABLES -A FORWARD -p TCP -i $LAN_IFACE -j ACCEPT
> $IPTABLES -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT
>
> ## Log weird packets that don't match the above.
> $IPTABLES -A FORWARD -m limit --limit 3/minute --limit-burst 3 -j LOG
> \
> --log-level DEBUG --log-prefix "IPT FORWARD packet died: "
>
>
> ######## OUTPUT chain ############
>
> # Bad TCP packets we don't want.
> $IPTABLES -A OUTPUT -p tcp -j bad_tcp_packets
>
> # Special OUTPUT rules to decide which IP's to allow.
> $IPTABLES -A OUTPUT -p ALL -s $LO_IP -j ACCEPT
> $IPTABLES -A OUTPUT -p ALL -s $LAN_IP_RANGE -j ACCEPT
> $IPTABLES -A OUTPUT -p ALL -s $INET_IP -j ACCEPT
>
> # Log weird packets that don't match the above.
> $IPTABLES -A OUTPUT -m limit --limit 3/minute --limit-burst 3 -j LOG \
> --log-level DEBUG --log-prefix "IPT OUTPUT packet died: "
>
>
> ### nat table
>
> ### Set policies
>
> ### Create user specified chains
>
> ### Create content in user specified chains
>
>
> ######## PREROUTING chain ##############
> # send packets from internet to web server
> $IPTABLES -t nat -A PREROUTING -p TCP -i $INET_IFACE -d $HTTP_IP
> --dport 80 -j DNAT --to-destination $DMZ_HTTP_IP
> $IPTABLES -t nat -A PREROUTING -p TCP -i $INET_IFACE -d $DNS_IP
> --dport 53 -j DNAT --to-destination $DMZ_DNS_IP
> $IPTABLES -t nat -A PREROUTING -p UDP -i $INET_IFACE -d $DNS_IP
> --dport 53 -j DNAT --to-destination $DMZ_DNS_IP
> $IPTABLES -t nat -A PREROUTING -p TCP -i $INET_IFACE -d $HTTP_IP
> --dport 22 -j DNAT --to-destination $DMZ_HTTP_IP
> $IPTABLES -t nat -A PREROUTING -p TCP -i $LAN_IFACE -d $INET_IP
> --dport 80 -j DNAT --to-destination $INET_IP
>
> ###### POSTROUTING chain ##############
> # Enable simple IP Forwarding and Network Address Translation
> $IPTABLES -t nat -A POSTROUTING -o $INET_IFACE -j SNAT --to-source
> $INET_IP
>
> ## OUTPUT chain
> # mangle table
> # Set policies
> # Create user specified chains
> # Create content in user specified chains
>
> # PREROUTING chain
> # INPUT chain
> # FORWARD chain
> # OUTPUT chain
> # POSTROUTING chain
>
>
> many thanks,
>
> james fox

www.ethereal.com

maybe you can see where it fails?



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