Hi there!
I am at the very beginning of using iptables.
I am using the example shown in netfilter howtos.
I checked all the settings and modified to my needs, but nothing: PC's under trusted subnet can't even get hostnames resolved. I read also the iptables tutorial, explaining the rc.firewall and everything seems to be right. I have no errors during rules setup.
I post the script that I am currently using:
1. Configuration options. #
# # 1.1 Internet Configuration. #
INET_IFACE="eth1"
# # 1.1.1 DHCP #
# # Information pertaining to DHCP over the Internet, if needed. # # Set DHCP variable to no if you don't get IP from DHCP. If you get DHCP # over the Internet set this variable to yes, and set up the proper IP # address for the DHCP server in the DHCP_SERVER variable. #
DHCP="no" DHCP_SERVER="192.168.0.241"
# # 1.1.2 PPPoE #
# Configuration options pertaining to PPPoE. # # If you have problem with your PPPoE connection, such as large mails not # getting through while small mail get through properly etc, you may set # this option to "yes" which may fix the problem. This option will set a # rule in the PREROUTING chain of the mangle table which will clamp # (resize) all routed packets to PMTU (Path Maximum Transmit Unit). # # Note that it is better to set this up in the PPPoE package itself, since # the PPPoE configuration option will give less overhead. #
PPPOE_PMTU="no"
# # 1.2 Local Area Network configuration. # # 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 #
LAN_IP="192.168.0.241" LAN_IP_RANGE="192.168.0.240/28" LAN_IFACE="eth0"
# # 1.3 DMZ Configuration. #
# # 1.4 Localhost Configuration. #
LO_IFACE="lo" LO_IP="127.0.0.1"
# # 1.5 IPTables Configuration. #
IPTABLES="/sbin/iptables"
# # 1.6 Other Configuration. #
########################################################################### # # 2. Module loading. #
# # Needed to initially load modules #
/sbin/depmod -a
# # 2.1 Required modules #
/sbin/modprobe ip_conntrack /sbin/modprobe ip_tables /sbin/modprobe iptable_filter /sbin/modprobe iptable_nat /sbin/modprobe ipt_LOG /sbin/modprobe ipt_limit /sbin/modprobe ipt_MASQUERADE
# # 2.2 Non-Required modules #
#/sbin/modprobe ipt_owner #/sbin/modprobe ipt_REJECT #/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
########################################################################### # # 4. rules set up. #
###### # 4.1 Filter table #
# # 4.1.1 Set policies #
$IPTABLES -P INPUT DROP $IPTABLES -P OUTPUT DROP $IPTABLES -P FORWARD DROP
# # 4.1.2 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 tcp_packets $IPTABLES -N udp_packets $IPTABLES -N icmp_packets
# # 4.1.3 Create content in userspecified chains #
# # bad_tcp_packets chain #
$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
# # 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
# # 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 80 -j allowed $IPTABLES -A tcp_packets -p TCP -s 0/0 --dport 113 -j allowed
# # UDP ports #
$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT if [ $DHCP == "yes" ] ; then $IPTABLES -A udp_packets -p UDP -s $DHCP_SERVER --sport 67 \ --dport 68 -j ACCEPT fi
#$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 53 -j ACCEPT #$IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 123 -j ACCEPT $IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 2074 -j ACCEPT $IPTABLES -A udp_packets -p UDP -s 0/0 --source-port 4000 -j ACCEPT
# # In Microsoft Networks you will be swamped by broadcasts. These lines # will prevent them from showing up in the logs. #
#$IPTABLES -A udp_packets -p UDP -i $INET_IFACE \ #--destination-port 135:139 -j DROP
# # If we get DHCP requests from the Outside of our network, our logs will # be swamped as well. This rule will block them from getting logged. #
#$IPTABLES -A udp_packets -p UDP -i $INET_IFACE -d 255.255.255.255 \ #--destination-port 67:68 -j DROP
# # ICMP rules #
$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
# # 4.1.4 INPUT chain #
# # Bad TCP packets we don't want. #
$IPTABLES -A INPUT -p tcp -j bad_tcp_packets
# # Rules for special networks not part of the Internet #
$IPTABLES -A INPUT -p ALL -i $LAN_IFACE -s $LAN_IP_RANGE -j ACCEPT $IPTABLES -A INPUT -p ALL -i $LO_IFACE -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
# # Rules for incoming packets from the internet. #
$IPTABLES -A INPUT -p ALL -i $INET_IFACE -m state --state ESTABLISHED,RELATED \
-j ACCEPT
$IPTABLES -A INPUT -p TCP -i $INET_IFACE -j tcp_packets
$IPTABLES -A INPUT -p UDP -i $INET_IFACE -j udp_packets
$IPTABLES -A INPUT -p ICMP -i $INET_IFACE -j icmp_packets
# # If you have a Microsoft Network on the outside of your firewall, you may # also get flooded by Multicasts. We drop them so we do not get flooded by # logs #
#$IPTABLES -A INPUT -i $INET_IFACE -d 224.0.0.0/8 -j DROP
# # 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: "
# # 4.1.5 FORWARD chain #
# # Bad TCP packets we don't want #
$IPTABLES -A FORWARD -p tcp -j bad_tcp_packets
# # Accept the packets we actually want to forward #
$IPTABLES -A FORWARD -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: "
# # 4.1.6 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 -j ACCEPT $IPTABLES -A OUTPUT -p ALL -o $INET_IFACE -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: "
###### # 4.2 nat table #
# # 4.2.1 Set policies #
# # 4.2.2 Create user specified chains #
# # 4.2.3 Create content in user specified chains #
# # 4.2.4 PREROUTING chain #
# # 4.2.5 POSTROUTING chain #
if [ $PPPOE_PMTU == "yes" ] ; then $IPTABLES -t nat -A POSTROUTING -p tcp --tcp-flags SYN,RST SYN \ -j TCPMSS --clamp-mss-to-pmtu fi $IPTABLES -t nat -A POSTROUTING -o $INET_IFACE -j MASQUERADE
#
