1 .\" Copyright (c) 2010 Maxim Ignatenko <gelraen.ua@gmail.com>
2 .\" Copyright (c) 2010 Vadim Goncharov <vadimnuclight@tpu.ru>
3 .\" Copyright (c) 2015 Dmitry Vagin <daemon.hammer@ya.ru>
4 .\" All rights reserved.
6 .\" Redistribution and use in source and binary forms, with or without
7 .\" modification, are permitted provided that the following conditions
9 .\" 1. Redistributions of source code must retain the above copyright
10 .\" notice, this list of conditions and the following disclaimer.
11 .\" 2. Redistributions in binary form must reproduce the above copyright
12 .\" notice, this list of conditions and the following disclaimer in the
13 .\" documentation and/or other materials provided with the distribution.
15 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 .Nd "trivial mbuf data modifying netgraph node type"
34 .In netgraph/ng_patch.h
38 node performs data modification of packets passing through it.
39 Modifications are restricted to a subset of C language operations
40 on unsigned integers of 8, 16, 32 or 64 bit size.
41 These are: set to new value (=), addition (+=), subtraction (-=),
42 multiplication (*=), division (/=), negation (= -),
43 bitwise AND (&=), bitwise OR (|=), bitwise eXclusive OR (^=),
44 shift left (<<=), shift right (>>=).
45 A negation operation is the one exception: integer is treated as signed
46 and second operand (the
49 If there is more than one modification operation, they are applied
50 to packets sequentially in the order they were specified by the user.
51 The data payload of a packet is viewed as an array of bytes, with a zero offset
52 corresponding to the very first byte of packet headers, and the
56 as a single integer in network byte order.
57 An additional offset can be optionally
58 requested at configuration time to account for packet type.
60 This node type has two hooks:
61 .Bl -tag -width ".Va out"
63 Packets received on this hook are modified according to rules specified
64 in the configuration and then forwarded to the
67 Otherwise they are reflected back to the
71 Packets received on this hook are forwarded to the
73 hook without any changes.
76 This node type supports the generic control messages, plus the following:
78 .It Dv NGM_PATCH_SETDLT Pq Ic setdlt
79 Sets the data link type on the
81 hook (to help calculate relative offset). Currently, supported types are
83 (raw IP datagrams , no offset applied, the default) and
85 (Ethernet). DLT_ definitions can be found in
87 If you want to work on the link layer header you must use no additional offset by specifying
91 is specified, then the optional additional offset will take into account the Ethernet header and a QinQ header if present.
92 .It Dv NGM_PATCH_GETDLT Pq Ic getdlt
93 This control message returns the data link type of the
96 .It Dv NGM_PATCH_SETCONFIG Pq Ic setconfig
97 This command sets the sequence of modify operations
98 that will be applied to incoming data on a hook.
100 .Vt "struct ng_patch_config"
101 must be supplied as an argument:
102 .Bd -literal -offset 4n
105 uint16_t length; /* 1,2,4 or 8 bytes */
110 #define NG_PATCH_MODE_SET 1
111 #define NG_PATCH_MODE_ADD 2
112 #define NG_PATCH_MODE_SUB 3
113 #define NG_PATCH_MODE_MUL 4
114 #define NG_PATCH_MODE_DIV 5
115 #define NG_PATCH_MODE_NEG 6
116 #define NG_PATCH_MODE_AND 7
117 #define NG_PATCH_MODE_OR 8
118 #define NG_PATCH_MODE_XOR 9
119 #define NG_PATCH_MODE_SHL 10
120 #define NG_PATCH_MODE_SHR 11
122 struct ng_patch_config {
125 uint32_t relative_offset;
126 struct ng_patch_op ops[];
132 can be set to any combination of CSUM_IP, CSUM_TCP, CSUM_SCTP and CSUM_UDP
133 (other values are ignored) for instructing the IP stack to recalculate the
134 corresponding checksum before transmitting packet on output interface.
137 node does not do any checksum correction by itself.
138 .It Dv NGM_PATCH_GETCONFIG Pq Ic getconfig
139 This control message returns the current set of modify operations,
141 .Vt "struct ng_patch_config" .
142 .It Dv NGM_PATCH_GET_STATS Pq Ic getstats
143 Returns the node's statistics as a
144 .Vt "struct ng_patch_stats" .
145 .It Dv NGM_PATCH_CLR_STATS Pq Ic clrstats
146 Clears the node's statistics.
147 .It Dv NGM_PATCH_GETCLR_STATS Pq Ic getclrstats
148 This command is identical to
149 .Dv NGM_PATCH_GET_STATS ,
150 except that the statistics are also atomically cleared.
153 This node shuts down upon receipt of a
155 control message, or when all hooks have been disconnected.
159 node was designed to modify TTL and TOS/DSCP fields in IP packets.
161 suppose you have two adjacent simplex links to a remote network
162 (e.g.\& satellite), so that the packets expiring in between
163 will generate unwanted ICMP-replies which have to go forth, not back.
164 Thus you need to raise TTL of every packet entering link by 2
165 to ensure the TTL will not reach zero there.
166 To achieve this you can set an
170 action to inject packets which are going to the simplex link into the patch node, by using the
174 .Bd -literal -offset 4n
175 /usr/sbin/ngctl -f- <<-SEQ
176 mkpeer ipfw: patch 200 in
177 name ipfw:200 ttl_add
178 msg ttl_add: setconfig { count=1 csum_flags=1 ops=[ \e
179 { mode=2 value=3 length=1 offset=8 } ] }
181 /sbin/ipfw add 150 netgraph 200 ip from any to simplex.remote.net
188 is configured to add (mode
189 .Dv NG_PATCH_MODE_ADD )
192 of 3 to a one-byte TTL field, which is 9th byte of IP packet header.
194 Another example would be two consecutive modifications of packet TOS
195 field: say, you need to clear the
201 .Bd -literal -offset 4n
202 /usr/sbin/ngctl -f- <<-SEQ
203 mkpeer ipfw: patch 300 in
204 name ipfw:300 tos_chg
205 msg tos_chg: setconfig { count=2 csum_flags=1 ops=[ \e
206 { mode=7 value=0xf7 length=1 offset=1 } \e
207 { mode=8 value=0x02 length=1 offset=1 } ] }
209 /sbin/ipfw add 160 netgraph 300 ip from any to any not dst-port 80
213 .Dv NG_PATCH_MODE_AND
214 clearing the fourth bit and then
216 setting the third bit.
220 field indicates that IP checksum (but not TCP or UDP checksum) should be
221 recalculated before transmit.
223 Note: one should ensure that packets are returned to ipfw after processing
226 by setting appropriate
229 .Bd -literal -offset 4n
230 sysctl net.inet.ip.fw.one_pass=0
239 node type was implemented in
242 .An "Maxim Ignatenko" Aq gelraen.ua@gmail.com .
244 Relative offset code by
247 This manual page was written by
248 .An "Vadim Goncharov" Aq vadimnuclight@tpu.ru .
250 The node blindly tries to apply every patching operation to each packet
251 (except those which offset if greater than length of the packet),
252 so be sure that you supply only the right packets to it (e.g. changing
253 bytes in the ARP packets meant to be in IP header could corrupt
254 them and make your machine unreachable from the network).
258 The output path of the IP stack assumes correct fields and lengths in the
259 packets - changing them by to incorrect values can cause
260 unpredictable results including kernel panics.