Example webserver iptable ruleset
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#! /bin/sh # /etc/iptables.bak # Let's save typing & confusion with variables IPTABLES=/sbin/iptables # Flush active rules and custom tables $IPTABLES --flush $IPTABLES --delete-chain # set the defaults so that by-default incoming packets are dropped, unless explicitly allowed; # for a desktop workstation, we'll let lots of (unpredictable) outgoing packets go freely. $IPTABLES -P INPUT DROP $IPTABLES -P FORWARD DROP $IPTABLES -P OUTPUT ACCEPT # INBOUND POLICY # ============== # of course, accepting loopback is a good idea $IPTABLES -A INPUT -i lo -j ACCEPT # we will permit ping, but rate-limit type 8 to prevent DoS-attack $IPTABLES -A INPUT -p icmp --icmp-type 0 -j ACCEPT $IPTABLES -A INPUT -p icmp --icmp-type 3 -j ACCEPT $IPTABLES -A INPUT -p icmp --icmp-type 11 -j ACCEPT $IPTABLES -A INPUT -p icmp --icmp-type 8 -m limit --limit 1/second -j ACCEPT # (Applies to packets entering our network interface from the network, # and addressed to this host.) $IPTABLES -A INPUT -m conntrack --ctstate INVALID -j DROP $IPTABLES -A INPUT -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT # ftp incoming $IPTABLES -A INPUT -p tcp -m conntrack --ctstate NEW --dport 20 -j ACCEPT $IPTABLES -A INPUT -p tcp -m conntrack --ctstate NEW --dport 21 -j ACCEPT # ssh incoming, including non-standard port (if needed) $IPTABLES -A INPUT -p tcp -m conntrack --ctstate NEW --dport 22 -j ACCEPT #$IPTABLES -A INPUT -p tcp -m conntrack --ctstate NEW --dport 222 -j ACCEPT # web serving, let's allow it! $IPTABLES -A INPUT -p tcp -m conntrack --ctstate NEW --dport 80 -j ACCEPT # secure web serving, let's allow it! $IPTABLES -A INPUT -p tcp -m conntrack --ctstate NEW --dport 443 -j ACCEPT # amanda tape-backups; we reach out and tape things from this machine $IPTABLES -A INPUT -p udp -m conntrack --ctstate NEW -m udp --dport 10080 -j ACCEPT $IPTABLES -A INPUT -p tcp -m conntrack --ctstate NEW --dport 10082 -j ACCEPT $IPTABLES -A INPUT -p tcp -m conntrack --ctstate NEW --dport 10083 -j ACCEPT # nagios (5666); monitor time (123), allow snmp (161) $IPTABLES -A INPUT -p tcp -m conntrack --ctstate NEW --dport 5666 -j ACCEPT $IPTABLES -A INPUT -p udp -m udp --dport 123 -j ACCEPT $IPTABLES -A INPUT -p udp -m udp --dport 161 -j ACCEPT # OUTBOUND POLICY # =============== # of course, accepting loopback is a good idea $IPTABLES -A OUTPUT -o lo -j ACCEPT # (Applies to packets sent to the network interface from local processes) $IPTABLES -A OUTPUT -j ACCEPT
Invoke and make these rules effective:
hostname ~ # sh /etc/iptables.bak
Resulting active rules:
hostname ~ # iptables -L
REMEMBER! If you like the ruleset, and want it to be in-effect the next time you start iptables (ie after a reboot), then you must:
hostname ~ # rc-update add iptables default * iptables added to runlevel default hostname ~ # /etc/init.d/iptables save * Saving iptables state ...