====== IPTables ======
FIXME
{{ :bpi-r2:network:firewall.png?nolink |}}
===== IPv4 =====
#delete previous rules
${ipt} -F
${ipt} -X
${ipt} -t nat -F
${ipt} -t nat -X
${ipt} -t mangle -F
${ipt} -t mangle -X
# Default-Rule for IPv4: drop all
${ipt} -P INPUT DROP
${ipt} -P OUTPUT DROP
${ipt} -P FORWARD DROP
# policy for TCP-Reset/UDP-Reject as alternative to "-j DROP"
${ipt} -N REJECTED
if [[ ! "${LOG}" = "" ]];
then
echo "enable IPv4-Firewall-Logging (all)...";
${ipt} -A REJECTED -m limit --limit 10/min -j LOG --log-prefix "NETFILTER4-REJECTED: " --log-level 4
fi
${ipt} -A REJECTED -p tcp -j REJECT --reject-with tcp-reset
${ipt} -A REJECTED -p udp -j REJECT --reject-with icmp-port-unreachable
${ipt} -A REJECTED -j DROP
# localhost
${ipt} -A INPUT -i lo -j ACCEPT
${ipt} -A OUTPUT -o lo -j ACCEPT
${ipt} -A OUTPUT -j ACCEPT
${ipt} -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT # incoming connetions which are requested
${ipt} -A INPUT -p icmp -m limit --limit 5/s --icmp-type echo-request -j ACCEPT # ICMP incoming, max 5/s
#Block Teredo-Stuff
#${ipt} -I FORWARD -p udp --dport 3544 -j REJECTED
#${ipt} -I FORWARD -p udp --sport 3544 -j REJECTED
#http://en.wikipedia.org/wiki/List_of_IP_protocol_numbers
${ipt} -A FORWARD -p 41 -j REJECTED #IPv6 Encapsulation
${ipt} -A FORWARD -p 43 -j REJECTED #Routing Header for IPv6
${ipt} -A FORWARD -p 44 -j REJECTED #Fragment Header for IPv6
${ipt} -A FORWARD -p 58 -j REJECTED #ICMP for IPv6
${ipt} -A FORWARD -p 59 -j REJECTED #No Next Header for IPv6
${ipt} -A FORWARD -p 60 -j REJECTED #Destination Options for IPv6
#ssh with rate-limit (replacing hosts.allow)
${ipt} -I INPUT -p tcp --dport 22 -i ${if_ext} -m state --state NEW -m recent --set
${ipt} -I INPUT -p tcp --dport 22 -i ${if_ext} -m state --state NEW -m recent --update --seconds 60 --hitcount 4 -j REJECTED #4 connections in 1 minute
${ipt} -A INPUT -p tcp --dport 22 -j ACCEPT #SSH incoming
${ipt} -A FORWARD -i ${if_int} -o ${if_ext} -j ACCEPT #Forwarding Int->Ext
${ipt} -A FORWARD -i ${if_ext} -o ${if_int} -m state --state ESTABLISHED,RELATED -j ACCEPT #Forwarding Ext->Int (only existing/requested connections)
${ipt} -A INPUT -i ${if_int} -j ACCEPT #accept all request from internal
... (some other rules, e.g. [[#port-forwardings]])
# REJECT/RESET for everything else
${ipt} -A INPUT -j REJECTED
${ipt} -A OUTPUT -j REJECTED
${ipt} -A FORWARD -j REJECTED
additional options:
#Kernel-option for SYN-Cookies
echo 1 > /proc/sys/net/ipv4/tcp_syncookies #enable syn cookies (prevent against 'syn flood attack')
if [ -f /proc/sys/net/ipv4/conf/all/accept_redirects ]; then
echo " Kernel ignores all ICMP redirects"
echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects
fi
if [ -f /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts ]; then
echo " Kernel ignores ICMP Echo requests sent to broadcast/multicast addresses"
echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
fi
==== Port-Forwardings ====
=== setup ===
forward port 522 to Client 192.168.0.5 port 22
${ipt} -t nat -A PREROUTING -p tcp --dport 522 -j DNAT --to-destination 192.168.0.5:22
=== show ===
iptables -L -t nat
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
DNAT tcp -- anywhere anywhere tcp dpt:522 to:192.168.0.5:22
==== active-ftp ====
to allow active-ftp from a client you need to load 2 modules and set 1 iptables-rule
modprobe ip_conntrack_ftp
modprobe ip_nat_ftp ports=21
${ipt} -A INPUT -p tcp --sport 20 -m state --state ESTABLISHED,RELATED -j ACCEPT
===== IPv6 =====