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>
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34 .Nd "trivial mbuf data modifying netgraph node type"
36 .In netgraph/ng_patch.h
40 node performs data modification of packets passing through it.
41 Modifications are restricted to a subset of C language operations
42 on unsigned integers of 8, 16, 32 or 64 bit size.
43 These are: set to new value (=), addition (+=), subtraction (-=),
44 multiplication (*=), division (/=), negation (= -),
45 bitwise AND (&=), bitwise OR (|=), bitwise eXclusive OR (^=),
46 shift left (<<=), shift right (>>=).
47 A negation operation is the one exception: integer is treated as signed
48 and second operand (the
51 If there is more than one modification operation, they are applied
52 to packets sequentially in the order they were specified by the user.
53 The data payload of a packet is viewed as an array of bytes, with a zero offset
54 corresponding to the very first byte of packet headers, and the
58 as a single integer in network byte order.
59 An additional offset can be optionally
60 requested at configuration time to account for packet type.
62 This node type has two hooks:
63 .Bl -tag -width ".Va out"
65 Packets received on this hook are modified according to rules specified
66 in the configuration and then forwarded to the
69 Otherwise they are reflected back to the
73 Packets received on this hook are forwarded to the
75 hook without any changes.
78 This node type supports the generic control messages, plus the following:
80 .It Dv NGM_PATCH_SETDLT Pq Ic setdlt
81 Sets the data link type on the
83 hook (to help calculate relative offset). Currently, supported types are
85 (raw IP datagrams , no offset applied, the default) and
87 (Ethernet). DLT_ definitions can be found in
89 If you want to work on the link layer header you must use no additional offset by specifying
93 is specified, then the optional additional offset will take into account the Ethernet header and a QinQ header if present.
94 .It Dv NGM_PATCH_GETDLT Pq Ic getdlt
95 This control message returns the data link type of the
98 .It Dv NGM_PATCH_SETCONFIG Pq Ic setconfig
99 This command sets the sequence of modify operations
100 that will be applied to incoming data on a hook.
102 .Vt "struct ng_patch_config"
103 must be supplied as an argument:
104 .Bd -literal -offset 4n
107 uint16_t length; /* 1,2,4 or 8 bytes */
112 #define NG_PATCH_MODE_SET 1
113 #define NG_PATCH_MODE_ADD 2
114 #define NG_PATCH_MODE_SUB 3
115 #define NG_PATCH_MODE_MUL 4
116 #define NG_PATCH_MODE_DIV 5
117 #define NG_PATCH_MODE_NEG 6
118 #define NG_PATCH_MODE_AND 7
119 #define NG_PATCH_MODE_OR 8
120 #define NG_PATCH_MODE_XOR 9
121 #define NG_PATCH_MODE_SHL 10
122 #define NG_PATCH_MODE_SHR 11
124 struct ng_patch_config {
127 uint32_t relative_offset;
128 struct ng_patch_op ops[];
134 can be set to any combination of CSUM_IP, CSUM_TCP, CSUM_SCTP and CSUM_UDP
135 (other values are ignored) for instructing the IP stack to recalculate the
136 corresponding checksum before transmitting packet on output interface.
139 node does not do any checksum correction by itself.
140 .It Dv NGM_PATCH_GETCONFIG Pq Ic getconfig
141 This control message returns the current set of modify operations,
143 .Vt "struct ng_patch_config" .
144 .It Dv NGM_PATCH_GET_STATS Pq Ic getstats
145 Returns the node's statistics as a
146 .Vt "struct ng_patch_stats" .
147 .It Dv NGM_PATCH_CLR_STATS Pq Ic clrstats
148 Clears the node's statistics.
149 .It Dv NGM_PATCH_GETCLR_STATS Pq Ic getclrstats
150 This command is identical to
151 .Dv NGM_PATCH_GET_STATS ,
152 except that the statistics are also atomically cleared.
155 This node shuts down upon receipt of a
157 control message, or when all hooks have been disconnected.
161 node was designed to modify TTL and TOS/DSCP fields in IP packets.
163 suppose you have two adjacent simplex links to a remote network
164 (e.g.\& satellite), so that the packets expiring in between
165 will generate unwanted ICMP-replies which have to go forth, not back.
166 Thus you need to raise TTL of every packet entering link by 2
167 to ensure the TTL will not reach zero there.
168 To achieve this you can set an
172 action to inject packets which are going to the simplex link into the patch node, by using the
176 .Bd -literal -offset 4n
177 /usr/sbin/ngctl -f- <<-SEQ
178 mkpeer ipfw: patch 200 in
179 name ipfw:200 ttl_add
180 msg ttl_add: setconfig { count=1 csum_flags=1 ops=[ \e
181 { mode=2 value=3 length=1 offset=8 } ] }
183 /sbin/ipfw add 150 netgraph 200 ip from any to simplex.remote.net
190 is configured to add (mode
191 .Dv NG_PATCH_MODE_ADD )
194 of 3 to a one-byte TTL field, which is 9th byte of IP packet header.
196 Another example would be two consecutive modifications of packet TOS
197 field: say, you need to clear the
203 .Bd -literal -offset 4n
204 /usr/sbin/ngctl -f- <<-SEQ
205 mkpeer ipfw: patch 300 in
206 name ipfw:300 tos_chg
207 msg tos_chg: setconfig { count=2 csum_flags=1 ops=[ \e
208 { mode=7 value=0xf7 length=1 offset=1 } \e
209 { mode=8 value=0x02 length=1 offset=1 } ] }
211 /sbin/ipfw add 160 netgraph 300 ip from any to any not dst-port 80
215 .Dv NG_PATCH_MODE_AND
216 clearing the fourth bit and then
218 setting the third bit.
222 field indicates that IP checksum (but not TCP or UDP checksum) should be
223 recalculated before transmit.
225 Note: one should ensure that packets are returned to ipfw after processing
228 by setting appropriate
231 .Bd -literal -offset 4n
232 sysctl net.inet.ip.fw.one_pass=0
241 node type was implemented in
244 .An "Maxim Ignatenko" Aq gelraen.ua@gmail.com .
246 Relative offset code by
249 This manual page was written by
250 .An "Vadim Goncharov" Aq vadimnuclight@tpu.ru .
252 The node blindly tries to apply every patching operation to each packet
253 (except those which offset if greater than length of the packet),
254 so be sure that you supply only the right packets to it (e.g. changing
255 bytes in the ARP packets meant to be in IP header could corrupt
256 them and make your machine unreachable from the network).
260 The output path of the IP stack assumes correct fields and lengths in the
261 packets - changing them by to incorrect values can cause
262 unpredictable results including kernel panics.