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1 perry 1 RAW
2 !!!RAW
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 ADDRESS FORMAT
7 SOCKET OPTIONS
8 NOTES
9 ERROR HANDLING
10 ERRORS
11 VERSIONS
12 BUGS
13 AUTHORS
14 SEE ALSO
15 ----
16 !!NAME
17
18
19 raw, SOCK_RAW - Linux IPv4 raw sockets
20 !!SYNOPSIS
21
22
23 __#include __
24 #include __
25 raw_socket = socket(PF_INET, SOCK_RAW, int__
26 ''protocol''__);__
27 !!DESCRIPTION
28
29
30 Raw sockets allow new IPv4 protocols to be implemented in
31 user space. A raw socket receives or sends the raw datagram
32 not including link level headers.
33
34
35 The IPv4 layer generates an IP header when sending a packet
36 unless the __IP_HDRINCL__ socket option is enabled on the
37 socket. When it is enabled, the packet must contain an IP
38 header. For receiving the IP header is always included in
39 the packet.
40
41
42 Only processes with an effective user id of 0 or the
43 __CAP_NET_RAW__ capability are allowed to open raw
44 sockets.
45
46
47 All packets or errors matching the ''protocol'' number
48 specified for the raw socket are passed to this socket. For
49 a list of the allowed protocols see RFC1700 assigned numbers
50 and getprotobyname(3).
51
52
53 A protocol of __IPPROTO_RAW__ implies enabled
54 __IP_HDRINCL__ and receives all IP protocols. Sending is
55 not allowed.
56
57
58 If __IP_HDRINCL__ is specified and the IP header has a non-zero destination address then the destination address of the socket is used to route the packet. When __MSG_DONTROUTE__ is specified the destination address should refer to a local interface, otherwise a routing table lookup is done anyways but gatewayed routes are ignored.
59
60
61 If __IP_HDRINCL__ isn't set then IP header options can be
62 set on raw sockets with setsockopt(2); see
63 ip(7) for more information.
64
65
66 In Linux 2.2 all IP header fields and options can be set
67 using IP socket options. This means raw sockets are usually
68 only needed for new protocols or protocols with no user
69 interface (like ICMP).
70
71
72 When a packet is received, it is passed to any raw sockets
73 which have been bound to its protocol before it is passed to
74 other protocol handlers (e.g. kernel protocol
75 modules).
76 !!ADDRESS FORMAT
77
78
79 Raw sockets use the standard __sockaddr_in__ address
80 structure defined in ip(7). The The __sin_port__
81 field could be used to specify the IP protocol number, but
82 it is ignored for sending in Linux 2.2 and should be always
83 set to 0 (see BUGS) For incoming packets __sin_port__ is
84 set to the protocol of the packet. See the
85 ____ include file for valid IP
86 protocols.
87 !!SOCKET OPTIONS
88
89
90 Raw socket options can be set with setsockopt(2) and
91 read with getsockopt(2) by passing the ''SOL_RAW''
92 family flag.
93
94
95 __ICMP_FILTER__
96
97
98 Enable a special filter for raw sockets bound to the
99 __IPPROTO_ICMP__ protocol. The value has a bit set for
100 each ICMP message type which should be filtered out. The
101 default is to filter no ICMP messages.
102
103
104 In addition all ip(7) __SOL_IP__ socket options
105 valid for datagram sockets are supported.
106 !!NOTES
107
108
109 Raw sockets fragment a packet when its total length exceeds
110 the interface MTU (but see BUGS). A more network friendly
111 and faster alternative is to implement path MTU discovery as
112 described in the __IP_PMTU_DISCOVER__ section of
113 ip(7).
114
115
116 A raw socket can be bound to a specific local address using
117 the bind(2) call. If it isn't bound all packets with
118 the specified IP protocol are received. In addition a RAW
119 socket can be bound to a specific network device using
120 __SO_BINDTODEVICE;__ see socket(7).
121
122
123 An __IPPROTO_RAW__ socket is send only. If you really
124 want to receive all IP packets use a packet(7) socket
125 with the __ETH_P_IP__ protocol. Note that packet sockets
126 don't reassemble IP fragments, unlike raw
127 sockets.
128
129
130 If you want to receive all ICMP packets for a datagram
131 socket it is often better to use __IP_RECVERR__ on that
132 particular socket; see ip(7).
133
134
135 Raw sockets may tap all IP protocols in Linux, even
136 protocols like ICMP or TCP which have a protocol module in
137 the kernel. In this case the packets are passed to both the
138 kernel module and the raw socket(s). This should not be
139 relied upon in portable programs, many other BSD socket
140 implementation have limitations here.
141
142
143 Linux never changes headers passed from the user (except for
144 filling in some zeroed fields as described for
145 __IP_HDRINCL__). This differs from many other
146 implementations of raw sockets.
147
148
149 RAW sockets are generally rather unportable and should be
150 avoided in programs intended to be portable.
151
152
153 Sending on raw sockets should take the IP protocol from
154 __sin_port;__ this ability was lost in Linux 2.2. Work
155 around is to use __IP_HDRINCL.__
156 !!ERROR HANDLING
157
158
159 Errors originating from the network are only passed to the
160 user when the socket is connected or the __IP_RECVERR__
161 flag is enabled. For connected sockets only __EMSGSIZE__
162 and __EPROTO__ are passed for compatibility. With
163 __IP_RECVERR__ all network errors are saved in the error
164 queue.
165 !!ERRORS
166
167
168 __EMSGSIZE__
169
170
171 Packet too big. Either Path MTU Discovery is enabled (the
172 __IP_PMTU_DISCOVER__ socket flag) or the packet size
173 exceeds the maximum allowed IPv4 packet size of
174 64KB.
175
176
177 __EACCES__
178
179
180 User tried to send to a broadcast address without having the
181 broadcast flag set on the socket.
182
183
184 __EPROTO__
185
186
187 An ICMP error has arrived reporting a parameter
188 problem.
189
190
191 __EFAULT__
192
193
194 An invalid memory address was supplied.
195
196
197 __EOPNOTSUPP__
198
199
200 Invalid flag has been passed to a socket call (like
201 __MSG_OOB__).
202
203
204 __EINVAL__
205
206
207 Invalid argument.
208
209
210 __EPERM__
211
212
213 The user doesn't have permission to open raw sockets. Only
214 processes with a effective user id of 0 or the
215 __CAP_NET_RAW__ attribute may do that.
216 !!VERSIONS
217
218
219 __IP_RECVERR__ and __ICMP_FILTER__ are new in Linux
220 2.2. They are Linux extensions and should not be used in
221 portable programs.
222
223
224 Linux 2.0 enabled some bug-to-bug compatibility with BSD in
225 the raw socket code when the SO_BSDCOMPAT flag was set -
226 that has been removed in 2.2.
227 !!BUGS
228
229
230 Transparent proxy extensions are not described.
231
232
233 When the __IP_HDRINCL__ option is set datagrams will not
234 be fragmented and are limited to the interface MTU. This is
235 a limitation in Linux 2.2.
236
237
238 Setting the IP protocol for sending in __sin_port__ got
239 lost in Linux 2.2. The protocol that socket was bound to or
240 that was specified in the initial socket(2) call is
241 always used.
242 !!AUTHORS
243
244
245 This man page was written by Andi Kleen.
246 !!SEE ALSO
247
248
249 ip(7), socket(7), recvmsg(2),
250 sendmsg(2)
251
252
253 __RFC1191__ for path MTU discovery.
254
255
256 __RFC791__ and the ____ include file
257 for the IP protocol.
258 ----
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