3 ### Classify packets according to source and destination networks.
5 ### (c) 2008 Mark Wooding
8 ###----- Licensing notice ---------------------------------------------------
10 ### This program is free software; you can redistribute it and/or modify
11 ### it under the terms of the GNU General Public License as published by
12 ### the Free Software Foundation; either version 2 of the License, or
13 ### (at your option) any later version.
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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 ### Address classification.
28 ### The objective of address classification is to work out what kind of
29 ### networks a packet is travelling between, in order to make filtering
32 ### Address classification is done in the mangle table, by attaching
33 ### appropriate marks to the packet. We split the Internet into a number of
34 ### address classes, and make forwarding decisions based on the classes of
35 ### the source and destination addresses.
37 ### The mark word is split into three fields: the FROM and TO fields simply
38 ### record the source and destination classes numerically; the MASK field is
39 ### used to determine whether forwarding should occur. There is a mask bit
40 ### for each address class. Source classification sets mask bits according
41 ### to the forwarding policy for the source address class. Destination
42 ### classification clears all of the mask bits except for the one
43 ### corresponding to the actual destination class. Therefore, forwarding is
44 ### permitted if and only if the mask bits are not all zero.
46 ### The mangle chains are arranged as follows.
48 ### The PREROUTING hook simply invokes in-classify and out-classify chains as
49 ### subroutines. These will tail-call appropriate classification chains.
51 ### The in-classify chain is responsible for both source address
52 ### classification and verifying that the packet arrived from the correct
53 ### interface. It does an initial dispatch on the source interface, to
54 ### in-IFACE. The in-IFACE chain dispatches to mark-from-CLASS when it
55 ### recognizes an address belonging to the CLASS; if no matches succeed, it
56 ### goes to bad-source-address, which logs a message and drops the packet.
57 ### The default interface is special. If no explicit matches are found, it
58 ### dispatches to in-default which forbids a few obviously evil things and
59 ### finally dispatches to mark-from-untrusted.
61 ### The out-classify is simpler because it doesn't care about the interface.
62 ### It simply checks each network range in turn, dispatching to mark-to-CLASS
63 ### on a match or mark-to-DEFAULT (probably untrusted) if there is no match.
65 clearchain mangle:in-classify mangle:in-default mangle:out-classify
66 clearchain mangle:local-source
68 ## Packets over the loopback interface are automatically trusted. All manner
69 ## of weird stuff happens on lo, and it's best not to second-guess it.
70 run ip46tables -t mangle -A in-classify -i lo -j ACCEPT
72 ## Local broadcast and link-local multicast packets sometimes have bizarre
73 ## addresses. Don't block them just because of this.
74 run iptables -t mangle -A in-classify -j RETURN \
75 -s 0.0.0.0 -d 255.255.255.255 \
77 run iptables -t mangle -A in-classify -j RETURN \
78 -s 0.0.0.0 -d 224.0.0.0/24 \
81 ## Since packets with source and destination addresses both local will go
82 ## over the loopback interface, I shouldn't see a packet from me over any
83 ## other interface. Except that I will if I sent a broadcast or multicast.
84 ## Allow the broadcasts, and remember not to trust them. There are no
85 ## broadcast addresses in IPv6 (only link-local multicast)m so we don't have
86 ## to worry about that.
87 run iptables -t mangle -A local-source -j RETURN \
88 -m addrtype --dst-type BROADCAST
89 run iptables -t mangle -A local-source -j RETURN \
90 -m addrtype --dst-type MULTICAST
91 run ip6tables -t mangle -A local-source -j RETURN \
93 run ip46tables -t mangle -A local-source -g bad-source-address
94 run iptables -t mangle -A in-classify -j local-source \
95 -m addrtype --src-type LOCAL
96 for addr in $host_6addrs; do
97 run ip6tables -t mangle -A in-classify -j local-source \
101 ## It's not valid to have a multicast address as a packet source: multicast
102 ## routing is done away from the source, so a multicast address would make
103 ## this impossible to do. So discard these packets. Also discard class-E
104 ## IPv4 addresses, since they aren't assigned.
105 run iptables -t mangle -A in-classify -g bad-source-address \
107 run ip6tables -t mangle -A in-classify -g bad-source-address \
111 ## Define the important networks.
118 ## Mark addresses reachable on non-default interfaces as not reachable on the
119 ## default interface.
120 trace "nets = $allnets $allnets6"
121 for net in $allnets; do
123 for iface in $defaultifaces; do
124 case $net in $iface:*) defaultp=t ;; esac
128 for iface in $defaultifaces; do
129 run iptables -t mangle -A in-$iface \
130 -s ${net#*:} -g bad-source-address
135 for net in $allnets6; do
137 for iface in $defaultifaces; do
138 case $net in $iface:*) defaultp=t ;; esac
142 for iface in $defaultifaces; do
143 run ip6tables -t mangle -A in-$iface \
144 -s ${net#*:} -g bad-source-address
150 ## Fill in the black holes in the network.
152 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \
153 127.0.0.0/8 192.0.2.0/24
155 run iptables -t mangle -A in-default -s $addr -g bad-source-address
161 run ip6tables -t mangle -A in-default -s $addr -g bad-source-address
165 ## Put the final default decision on the in-default chain, and attach the
166 ## classification chains to the PREROUTING hook.
167 for iface in $defaultifaces; do
168 run ip46tables -t mangle -A in-$iface -g mark-from-$defaultclass
170 run ip46tables -t mangle -A out-classify -g mark-to-$defaultclass
171 run ip46tables -t mangle -A PREROUTING -j in-classify
172 run ip46tables -t mangle -A PREROUTING -j out-classify
174 ## Now it's safe to let stuff through.
175 for i in PREROUTING INPUT FORWARD OUTPUT POSTROUTING; do
176 run ip46tables -t mangle -P $i ACCEPT
180 ###----- That's all, folks --------------------------------------------------