3 ### Initialization and finishing touches for firewall scripts
5 ### (c) 2008 Mark Wooding
8 ###----- Licensing notice ---------------------------------------------------
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18 ### GNU General Public License for more details.
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22 ### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
25 ###--------------------------------------------------------------------------
26 ### Clear existing firewall rules.
28 ## The main chains: set policy to drop, and then clear the rules. For a
29 ## while, incoming packets will be silently dropped, but we should have got
30 ## everything going before anyone actually hits a timeout.
31 for t in mangle filter; do
32 for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
33 run iptables -t $t -P $i DROP 2>/dev/null || :
34 run iptables -t $t -F $i 2>/dev/null || :
41 ###--------------------------------------------------------------------------
42 ### Set safe IP options.
44 ## Set forwarding options. Apparently setting ip_forward clobbers other
45 ## settings, so put this first.
46 setopt ip_forward $forward
47 setdevopt forwarding $forward
49 ## Set dynamic port allocation.
50 setopt ip_local_port_range $open_port_min $open_port_max
52 ## Deploy SYN-cookies if necessary.
53 setopt tcp_syncookies 1
55 ## Turn on the reverse-path filter, and log weird things.
57 setdevopt log_martians 1
59 ## Turn off things which can mess with our routing decisions.
60 setdevopt accept_source_route 0
61 setdevopt accept_redirects 0
63 ## If we're maent to stop the firewall, then now is the time to do it.
67 ###--------------------------------------------------------------------------
68 ### Establish error chains.
70 errorchain forbidden REJECT --reject-with icmp-host-prohibited
71 ## Generic `not allowed' chain. Rejects with ICMP host-prohibited.
73 errorchain tcp-fragment REJECT --reject-with icmp-host-prohibited
74 ## Chain for logging fragmented TCP segements. Rejects with ICMP
77 errorchain bad-tcp REJECT -p tcp --reject-with tcp-reset
78 ## Bad TCP segments (e.g., for unknown connections). Sends a TCP reset.
80 errorchain mangle:bad-source-address DROP
81 ## Packet arrived on wrong interface for its source address. Drops the
82 ## packet, since there's nowhere sensible to send an error.
84 errorchain bad-destination-address REJECT --reject-with icmp-host-prohibited
85 ## Packet arrived on non-loopback interface with loopback destination. Sends
88 errorchain interesting ACCEPT
89 ## Not an error, just log interesting packets.
92 ###--------------------------------------------------------------------------
93 ### Standard loopback stuff.
95 ## Don't clobber local traffic
96 run iptables -A INPUT -i lo -j ACCEPT
98 ## We really shouldn't see packets destined for localhost on any interface
99 ## other than the loopback.
100 run iptables -A INPUT -g bad-destination-address \
104 ###--------------------------------------------------------------------------
105 ### Finishing touches.
108 ## Locally generated packets are all OK.
109 run iptables -P OUTPUT ACCEPT
111 ## Other incoming things are forbidden.
112 for chain in INPUT FORWARD; do
113 run iptables -A $chain -g forbidden
117 ###----- That's all, folks --------------------------------------------------