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28 .\" @(#)netintro.4 8.2 (Berkeley) 11/30/93
29 .\" $FreeBSD: src/share/man/man4/netintro.4,v 1.10.2.6 2002/08/30 14:23:38 sobomax Exp $
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31 .Dd May 29, 2022
32 .Dt NETINTRO 4
33 .Os
34 .Sh NAME
35 .Nm networking
36 .Nd introduction to networking facilities
37 .Sh SYNOPSIS
38 .In sys/types.h
39 .In sys/time.h
40 .In sys/socket.h
41 .In net/if.h
42 .In net/route.h
43 .Sh DESCRIPTION
44 This section is a general introduction to the networking facilities
45 available in the system.
46 Documentation in this part of section
47 4 is broken up into three areas:
48 .Em protocol families
49 (domains),
50 .Em protocols ,
51 and
52 .Em network interfaces .
53 .Pp
54 All network protocols are associated with a specific
55 .Em protocol family .
56 A protocol family provides basic services to the protocol
57 implementation to allow it to function within a specific
58 network environment. These services may include
59 packet fragmentation and reassembly, routing, addressing, and
60 basic transport. A protocol family may support multiple
61 methods of addressing, though the current protocol implementations
62 do not. A protocol family is normally comprised of a number
63 of protocols, one per
64 .Xr socket 2
65 type. It is not required that a protocol family support
66 all socket types. A protocol family may contain multiple
67 protocols supporting the same socket abstraction.
68 .Pp
69 A protocol supports one of the socket abstractions detailed in
70 .Xr socket 2 .
71 A specific protocol may be accessed either by creating a
72 socket of the appropriate type and protocol family, or
73 by requesting the protocol explicitly when creating a socket.
74 Protocols normally accept only one type of address format,
75 usually determined by the addressing structure inherent in
76 the design of the protocol family/network architecture.
77 Certain semantics of the basic socket abstractions are
78 protocol specific. All protocols are expected to support
79 the basic model for their particular socket type, but may,
80 in addition, provide non-standard facilities or extensions
81 to a mechanism. For example, a protocol supporting the
82 .Dv SOCK_STREAM
83 abstraction may allow more than one byte of out-of-band
84 data to be transmitted per out-of-band message.
85 .Pp
86 A network interface is similar to a device interface.
87 Network interfaces comprise the lowest layer of the
88 networking subsystem, interacting with the actual transport
89 hardware. An interface may support one or more protocol
90 families and/or address formats.
91 The SYNOPSIS section of each network interface
92 entry gives a sample specification
93 of the related drivers for use in the kernel configuration file.
94 The DIAGNOSTICS section lists messages which may appear on the console
95 and/or in the system error log,
96 .Pa /var/log/messages
97 (see
98 .Xr syslogd 8 ) ,
99 due to errors in device operation.
100 .Sh PROTOCOLS
101 The system currently supports the
102 Internet
103 protocols, the Xerox Network Systems(tm) protocols,
104 and some of the
105 .Tn ISO OSI
106 protocols.
107 Raw socket interfaces are provided to the
108 .Tn IP
109 protocol
110 layer of the
111 Internet, and to the
112 .Tn IDP
113 protocol of Xerox
114 .Tn NS .
115 Consult the appropriate manual pages in this section for more
116 information regarding the support for each protocol family.
117 .Sh ADDRESSING
118 Associated with each protocol family is an address
119 format. All network address adhere to a general structure,
120 called a sockaddr, described below.
121 However, each protocol
122 imposes finer and more specific structure, generally renaming
123 the variant, which is discussed in the protocol family manual
124 page alluded to above.
125 .Bd -literal -offset indent
126 struct sockaddr {
127 u_char sa_len;
128 u_char sa_family;
129 char sa_data[14];
130 };
131 .Ed
132 .Pp
133 The field
134 .Va sa_len
135 contains the total length of the structure,
136 which may exceed 16 bytes.
137 The following address values for
138 .Va sa_family
139 are known to the system
140 (and additional formats are defined for possible future implementation):
141 .Bd -literal
142 #define AF_UNIX 1 /* local to host (pipes, portals) */
143 #define AF_INET 2 /* internetwork: UDP, TCP, etc. */
144 #define AF_CCITT 10 /* CCITT protocols, X.25 etc */
145 #define AF_HYLINK 15 /* NSC Hyperchannel */
146 .Ed
147 .Sh ROUTING
148 .Ux
149 provides some packet routing facilities.
150 The kernel maintains a routing information database, which
151 is used in selecting the appropriate network interface when
152 transmitting packets.
153 .Pp
154 A user process (or possibly multiple co-operating processes)
155 maintains this database by sending messages over a special kind
156 of socket.
157 This supplants fixed size
158 .Xr ioctl 2
159 used in earlier releases.
160 .Pp
161 This facility is described in
162 .Xr route 4 .
163 .Sh INTERFACES
164 Each network interface in a system corresponds to a
165 path through which messages may be sent and received. A network
166 interface usually has a hardware device associated with it, though
167 certain interfaces such as the loopback interface,
168 .Xr lo 4 ,
169 do not.
170 .Pp
171 The following
172 .Xr ioctl 2
173 calls may be used to manipulate network interfaces.
174 The
175 .Fn ioctl
176 is made on a socket (typically of type
177 .Dv SOCK_DGRAM )
178 in the desired domain.
179 Most of the requests supported in earlier releases
180 take an
181 .Vt ifreq
182 structure as its parameter. This structure has the form
183 .Bd -literal
184 struct ifreq {
185 #define IFNAMSIZ 16
186 char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */
187 union {
188 struct sockaddr ifru_addr;
189 struct sockaddr ifru_dstaddr;
190 struct sockaddr ifru_broadaddr;
191 struct ifreq_buffer ifru_buffer;
192 short ifru_flags[2];
193 int ifru_metric;
194 int ifru_mtu;
195 int ifru_phys;
196 caddr_t ifru_data;
197 } ifr_ifru;
198 #define ifr_addr ifr_ifru.ifru_addr /* address */
199 #define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
200 #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
201 #define ifr_buffer ifr_ifru.ifru_buffer /* user supplied buffer with its length */
202 #define ifr_flags ifr_ifru.ifru_flags[0] /* flags (low 16 bits) */
203 #define ifr_flagshigh ifr_ifru.ifru_flags[1] /* flags (high 16 bits) */
204 #define ifr_metric ifr_ifru.ifru_metric /* metric */
205 #define ifr_mtu ifr_ifru.ifru_mtu /* mtu */
206 #define ifr_phys ifr_ifru.ifru_phys /* physical wire */
207 #define ifr_data ifr_ifru.ifru_data /* for use by interface */
208 };
209 .Ed
210 .Pp
211 Calls which are now deprecated are:
212 .Bl -tag -width ".Dv SIOCGIFBRDADDR"
213 .It Dv SIOCSIFADDR
214 Set interface address for protocol family. Following the address
215 assignment, the ``initialization'' routine for
216 the interface is called.
217 .It Dv SIOCSIFDSTADDR
218 Set point to point address for protocol family and interface.
219 .It Dv SIOCSIFBRDADDR
220 Set broadcast address for protocol family and interface.
221 .El
222 .Pp
223 .Fn Ioctl
224 requests to obtain addresses and requests both to set and
225 retrieve other data are still fully supported
226 and use the
227 .Vt ifreq
228 structure:
229 .Bl -tag -width ".Dv SIOCGIFBRDADDR"
230 .It Dv SIOCGIFADDR
231 Get interface address for protocol family.
232 .It Dv SIOCGIFDSTADDR
233 Get point to point address for protocol family and interface.
234 .It Dv SIOCGIFBRDADDR
235 Get broadcast address for protocol family and interface.
236 .It Dv SIOCGIFDESCR
237 Get the interface description, returned in the
238 .Va buffer
239 field of
240 .Va ifru_buffer
241 struct.
242 The user supplied buffer length should be defined in the
243 .Va length
244 field of
245 .Va ifru_buffer
246 struct passed in as parameter, and the length would include
247 the terminating nul character.
248 If there is not enough space to hold the interface description,
249 no copy would be done and an error would be returned.
250 The kernel will store the required buffer length in the
251 .Va length
252 field upon return, regardless whether the buffer itself is
253 sufficient to hold the data.
254 .It Dv SIOCSIFDESCR
255 Set the interface description to the value of the
256 .Va buffer
257 field of
258 .Va ifru_buffer
259 struct, with
260 .Va length
261 field specifying its length (counting the terminating nul).
262 .It Dv SIOCSIFFLAGS
263 Set interface flags field. If the interface is marked down,
264 any processes currently routing packets through the interface
265 are notified;
266 some interfaces may be reset so that incoming packets are no longer received.
267 When marked up again, the interface is reinitialized.
268 .It Dv SIOCGIFFLAGS
269 Get interface flags.
270 .It Dv SIOCSIFMETRIC
271 Set interface routing metric.
272 The metric is used only by user-level routers.
273 .It Dv SIOCGIFMETRIC
274 Get interface metric.
275 .It Dv SIOCIFCREATE
276 Attempt to create the specified interface.
277 If the interface name is given without a unit number the system
278 will attempt to create a new interface with an arbitrary unit number.
279 On successful return the
280 .Va ifr_name
281 field will contain the new interface name.
282 .It Dv SIOCIFDESTROY
283 Attempt to destroy the specified interface.
284 .El
285 .Pp
286 There are two requests that make use of a new structure:
287 .Bl -tag -width ".Dv SIOCGIFBRDADDR"
288 .It Dv SIOCAIFADDR
289 An interface may have more than one address associated with it
290 in some protocols. This request provides a means to
291 add additional addresses (or modify characteristics of the
292 primary address if the default address for the address family
293 is specified). Rather than making separate calls to
294 set destination or broadcast addresses, or network masks
295 (now an integral feature of multiple protocols)
296 a separate structure is used to specify all three facets simultaneously
297 (see below).
298 One would use a slightly tailored version of this struct specific
299 to each family (replacing each sockaddr by one
300 of the family-specific type).
301 Where the sockaddr itself is larger than the
302 default size, one needs to modify the
303 .Fn ioctl
304 identifier itself to include the total size, as described in
305 .Fn ioctl .
306 .It Dv SIOCDIFADDR
307 This requests deletes the specified address from the list
308 associated with an interface. It also uses the
309 .Vt ifaliasreq
310 structure to allow for the possibility of protocols allowing
311 multiple masks or destination addresses, and also adopts the
312 convention that specification of the default address means
313 to delete the first address for the interface belonging to
314 the address family in which the original socket was opened.
315 .It Dv SIOCGIFALIAS
316 This request provides means to get additional addresses
317 together with netmask and broadcast/destination from an
318 interface.
319 It also uses the
320 .Vt ifaliasreq
321 structure.
322 .It Dv SIOCGIFCONF
323 Get interface configuration list. This request takes an
324 .Vt ifconf
325 structure (see below) as a value-result parameter. The
326 .Va ifc_len
327 field should be initially set to the size of the buffer
328 pointed to by
329 .Va ifc_buf .
330 On return it will contain the length, in bytes, of the
331 configuration list.
332 .It Dv SIOCIFGCLONERS
333 Get list of clonable interfaces.
334 This request takes an
335 .Vt if_clonereq
336 structure (see below) as a value-result parameter.
337 The
338 .Va ifcr_count
339 field should be set to the number of
340 .Dv IFNAMSIZ
341 sized strings that can be fit in the buffer pointed to by
342 .Va ifcr_buffer .
343 On return,
344 .Va ifcr_total
345 will be set to the number of clonable interfaces and the buffer pointed
346 to by
347 .Va ifcr_buffer
348 will be filled with the names of clonable interfaces aligned on
349 .Dv IFNAMSIZ
350 boundaries.
351 .El
352 .Bd -literal
353 /*
354 * Structure used in SIOCAIFCONF request.
355 */
356 struct ifaliasreq {
357 char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
358 struct sockaddr ifra_addr;
359 struct sockaddr ifra_broadaddr;
360 struct sockaddr ifra_mask;
361 };
362 .Ed
363 .Bd -literal
364 /*
365 * Structure used in SIOCGIFCONF request.
366 * Used to retrieve interface configuration
367 * for machine (useful for programs which
368 * must know all networks accessible).
369 */
370 struct ifconf {
371 int ifc_len; /* size of associated buffer */
372 union {
373 caddr_t ifcu_buf;
374 struct ifreq *ifcu_req;
375 } ifc_ifcu;
376 #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
377 #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
378 };
379 .Ed
380 .Bd -literal
381 /* Structure used in SIOCIFGCLONERS request. */
382 struct if_clonereq {
383 int ifcr_total; /* total cloners (out) */
384 int ifcr_count; /* room for this many in user buffer */
385 char *ifcr_buffer; /* buffer for cloner names */
386 };
387 .Ed
388 .Bd -literal
389 /* Structure used in SIOCGIFDESCR and SIOCSIFDESCR requests */
390 struct ifreq_buffer {
391 size_t length; /* length of the buffer */
392 void *buffer; /* pointer to userland space buffer */
393 };
394 .Ed
395 .Sh SEE ALSO
396 .Xr ioctl 2 ,
397 .Xr socket 2 ,
398 .Xr intro 4 ,
399 .Xr routed 8
400 .Sh HISTORY
401 The
402 .Nm netintro
403 manual appeared in
404 .Bx 4.3 tahoe .