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32 .\" @(#)netintro.4 8.2 (Berkeley) 11/30/93
33 .\" $FreeBSD$
34 .\"
35 .Dd June 18, 2004
36 .Dt NETINTRO 4
37 .Os
38 .Sh NAME
39 .Nm networking
40 .Nd introduction to networking facilities
41 .Sh SYNOPSIS
42 .In sys/types.h
43 .In sys/time.h
44 .In sys/socket.h
45 .In net/if.h
46 .In net/route.h
47 .Sh DESCRIPTION
48 This section is a general introduction to the networking facilities
49 available in the system.
50 Documentation in this part of section
51 4 is broken up into three areas:
52 .Em protocol families
53 (domains),
54 .Em protocols ,
55 and
56 .Em network interfaces .
57 .Pp
58 All network protocols are associated with a specific
59 .Em protocol family .
60 A protocol family provides basic services to the protocol
61 implementation to allow it to function within a specific
62 network environment.
63 These services may include
64 packet fragmentation and reassembly, routing, addressing, and
65 basic transport.
66 A protocol family may support multiple
67 methods of addressing, though the current protocol implementations
68 do not.
69 A protocol family is normally comprised of a number of protocols, one per
70 .Xr socket 2
71 type.
72 It is not required that a protocol family support all socket types.
73 A protocol family may contain multiple
74 protocols supporting the same socket abstraction.
75 .Pp
76 A protocol supports one of the socket abstractions detailed in
77 .Xr socket 2 .
78 A specific protocol may be accessed either by creating a
79 socket of the appropriate type and protocol family, or
80 by requesting the protocol explicitly when creating a socket.
81 Protocols normally accept only one type of address format,
82 usually determined by the addressing structure inherent in
83 the design of the protocol family/network architecture.
84 Certain semantics of the basic socket abstractions are
85 protocol specific.
86 All protocols are expected to support
87 the basic model for their particular socket type, but may,
88 in addition, provide non-standard facilities or extensions
89 to a mechanism.
90 For example, a protocol supporting the
91 .Dv SOCK_STREAM
92 abstraction may allow more than one byte of out-of-band
93 data to be transmitted per out-of-band message.
94 .Pp
95 A network interface is similar to a device interface.
96 Network interfaces comprise the lowest layer of the
97 networking subsystem, interacting with the actual transport
98 hardware.
99 An interface may support one or more protocol families and/or address formats.
100 The SYNOPSIS section of each network interface
101 entry gives a sample specification
102 of the related drivers for use in providing
103 a system description to the
104 .Xr config 8
105 program.
106 The DIAGNOSTICS section lists messages which may appear on the console
107 and/or in the system error log,
108 .Pa /var/log/messages
109 (see
110 .Xr syslogd 8 ) ,
111 due to errors in device operation.
112 .Sh PROTOCOLS
113 The system currently supports the
114 Internet
115 protocols, the Xerox Network Systems(tm) protocols,
116 and some of the
117 .Tn ISO OSI
118 protocols.
119 Raw socket interfaces are provided to the
120 .Tn IP
121 protocol
122 layer of the
123 Internet, and to the
124 .Tn IDP
125 protocol of Xerox
126 .Tn NS .
127 Consult the appropriate manual pages in this section for more
128 information regarding the support for each protocol family.
129 .Sh ADDRESSING
130 Associated with each protocol family is an address
131 format.
132 All network addresses adhere to a general structure,
133 called a sockaddr, described below.
134 However, each protocol
135 imposes finer and more specific structure, generally renaming
136 the variant, which is discussed in the protocol family manual
137 page alluded to above.
138 .Bd -literal -offset indent
139 struct sockaddr {
140 u_char sa_len;
141 u_char sa_family;
142 char sa_data[14];
143 };
144 .Ed
145 .Pp
146 The field
147 .Va sa_len
148 contains the total length of the structure,
149 which may exceed 16 bytes.
150 The following address values for
151 .Va sa_family
152 are known to the system
153 (and additional formats are defined for possible future implementation):
154 .Bd -literal
155 #define AF_UNIX 1 /* local to host (pipes, portals) */
156 #define AF_INET 2 /* internetwork: UDP, TCP, etc. */
157 #define AF_NS 6 /* Xerox NS protocols */
158 #define AF_CCITT 10 /* CCITT protocols, X.25 etc */
159 #define AF_HYLINK 15 /* NSC Hyperchannel */
160 #define AF_ISO 18 /* ISO protocols */
161 .Ed
162 .Sh ROUTING
163 .Fx
164 provides some packet routing facilities.
165 The kernel maintains a routing information database, which
166 is used in selecting the appropriate network interface when
167 transmitting packets.
168 .Pp
169 A user process (or possibly multiple co-operating processes)
170 maintains this database by sending messages over a special kind
171 of socket.
172 This supplants fixed size
173 .Xr ioctl 2
174 used in earlier releases.
175 .Pp
176 This facility is described in
177 .Xr route 4 .
178 .Sh INTERFACES
179 Each network interface in a system corresponds to a
180 path through which messages may be sent and received.
181 A network interface usually has a hardware device associated with it, though
182 certain interfaces such as the loopback interface,
183 .Xr lo 4 ,
184 do not.
185 .Pp
186 The following
187 .Xr ioctl 2
188 calls may be used to manipulate network interfaces.
189 The
190 .Fn ioctl
191 is made on a socket (typically of type
192 .Dv SOCK_DGRAM )
193 in the desired domain.
194 Most of the requests supported in earlier releases
195 take an
196 .Vt ifreq
197 structure as its parameter.
198 This structure has the form
199 .Bd -literal
200 struct ifreq {
201 #define IFNAMSIZ 16
202 char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */
203 union {
204 struct sockaddr ifru_addr;
205 struct sockaddr ifru_dstaddr;
206 struct sockaddr ifru_broadaddr;
207 short ifru_flags[2];
208 short ifru_index;
209 int ifru_metric;
210 int ifru_mtu;
211 int ifru_phys;
212 int ifru_media;
213 caddr_t ifru_data;
214 int ifru_cap[2];
215 } ifr_ifru;
216 #define ifr_addr ifr_ifru.ifru_addr /* address */
217 #define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
218 #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
219 #define ifr_flags ifr_ifru.ifru_flags[0] /* flags (low 16 bits) */
220 #define ifr_flagshigh ifr_ifru.ifru_flags[1] /* flags (high 16 bits) */
221 #define ifr_metric ifr_ifru.ifru_metric /* metric */
222 #define ifr_mtu ifr_ifru.ifru_mtu /* mtu */
223 #define ifr_phys ifr_ifru.ifru_phys /* physical wire */
224 #define ifr_media ifr_ifru.ifru_media /* physical media */
225 #define ifr_data ifr_ifru.ifru_data /* for use by interface */
226 #define ifr_reqcap ifr_ifru.ifru_cap[0] /* requested capabilities */
227 #define ifr_curcap ifr_ifru.ifru_cap[1] /* current capabilities */
228 #define ifr_index ifr_ifru.ifru_index /* interface index */
229 };
230 .Ed
231 .Pp
232 Calls which are now deprecated are:
233 .Bl -tag -width SIOCGIFBRDADDR
234 .It Dv SIOCSIFADDR
235 Set interface address for protocol family.
236 Following the address assignment, the
237 .Dq initialization
238 routine for the interface is called.
239 .It Dv SIOCSIFDSTADDR
240 Set point to point address for protocol family and interface.
241 .It Dv SIOCSIFBRDADDR
242 Set broadcast address for protocol family and interface.
243 .El
244 .Pp
245 .Fn Ioctl
246 requests to obtain addresses and requests both to set and
247 retrieve other data are still fully supported
248 and use the
249 .Vt ifreq
250 structure:
251 .Bl -tag -width SIOCGIFBRDADDR
252 .It Dv SIOCGIFADDR
253 Get interface address for protocol family.
254 .It Dv SIOCGIFDSTADDR
255 Get point to point address for protocol family and interface.
256 .It Dv SIOCGIFBRDADDR
257 Get broadcast address for protocol family and interface.
258 .It Dv SIOCSIFCAP
259 Attempt to set the enabled capabilities field for the interface
260 to the value of the
261 .Va ifr_reqcap
262 field of the
263 .Vt ifreq
264 structure.
265 Note that, depending on the particular interface features,
266 some capabilities may appear hard-coded to enabled, or toggling
267 a capability may affect the status of other ones.
268 The supported capabilities field is read-only, and the
269 .Va ifr_curcap
270 field is unused by this call.
271 .It Dv SIOCGIFCAP
272 Get the interface capabilities fields.
273 The values for supported and enabled capabilities will be returned in the
274 .Va ifr_reqcap
275 and
276 .Va ifr_curcap
277 fields of the
278 .Vt ifreq
279 structure, respectively.
280 .It Dv SIOCSIFFLAGS
281 Set interface flags field.
282 If the interface is marked down,
283 any processes currently routing packets through the interface
284 are notified;
285 some interfaces may be reset so that incoming packets are no longer received.
286 When marked up again, the interface is reinitialized.
287 .It Dv SIOCGIFFLAGS
288 Get interface flags.
289 .It Dv SIOCSIFMETRIC
290 Set interface routing metric.
291 The metric is used only by user-level routers.
292 .It Dv SIOCGIFMETRIC
293 Get interface metric.
294 .It Dv SIOCIFCREATE
295 Attempt to create the specified interface.
296 If the interface name is given without a unit number the system
297 will attempt to create a new interface with an arbitrary unit number.
298 On successful return the
299 .Va ifr_name
300 field will contain the new interface name.
301 .It Dv SIOCIFDESTROY
302 Attempt to destroy the specified interface.
303 .El
304 .Pp
305 There are two requests that make use of a new structure:
306 .Bl -tag -width SIOCGIFBRDADDR
307 .It Dv SIOCAIFADDR
308 An interface may have more than one address associated with it
309 in some protocols.
310 This request provides a means to
311 add additional addresses (or modify characteristics of the
312 primary address if the default address for the address family
313 is specified).
314 Rather than making separate calls to
315 set destination or broadcast addresses, or network masks
316 (now an integral feature of multiple protocols)
317 a separate structure is used to specify all three facets simultaneously
318 (see below).
319 One would use a slightly tailored version of this struct specific
320 to each family (replacing each sockaddr by one
321 of the family-specific type).
322 Where the sockaddr itself is larger than the
323 default size, one needs to modify the
324 .Fn ioctl
325 identifier itself to include the total size, as described in
326 .Fn ioctl .
327 .It Dv SIOCDIFADDR
328 This requests deletes the specified address from the list
329 associated with an interface.
330 It also uses the
331 .Vt ifaliasreq
332 structure to allow for the possibility of protocols allowing
333 multiple masks or destination addresses, and also adopts the
334 convention that specification of the default address means
335 to delete the first address for the interface belonging to
336 the address family in which the original socket was opened.
337 .It Dv SIOCGIFCONF
338 Get interface configuration list.
339 This request takes an
340 .Vt ifconf
341 structure (see below) as a value-result parameter.
342 The
343 .Va ifc_len
344 field should be initially set to the size of the buffer
345 pointed to by
346 .Va ifc_buf .
347 On return it will contain the length, in bytes, of the
348 configuration list.
349 .It Dv SIOCIFGCLONERS
350 Get list of clonable interfaces.
351 This request takes an
352 .Vt if_clonereq
353 structure (see below) as a value-result parameter.
354 The
355 .Va ifcr_count
356 field should be set to the number of
357 .Dv IFNAMSIZ
358 sized strings that can be fit in the buffer pointed to by
359 .Va ifcr_buffer .
360 On return,
361 .Va ifcr_total
362 will be set to the number of clonable interfaces and the buffer pointed
363 to by
364 .Va ifcr_buffer
365 will be filled with the names of clonable interfaces aligned on
366 .Dv IFNAMSIZ
367 boundaries.
368 .El
369 .Bd -literal
370 /*
371 * Structure used in SIOCAIFCONF request.
372 */
373 struct ifaliasreq {
374 char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
375 struct sockaddr ifra_addr;
376 struct sockaddr ifra_broadaddr;
377 struct sockaddr ifra_mask;
378 };
379 .Ed
380 .Pp
381 .Bd -literal
382 /*
383 * Structure used in SIOCGIFCONF request.
384 * Used to retrieve interface configuration
385 * for machine (useful for programs which
386 * must know all networks accessible).
387 */
388 struct ifconf {
389 int ifc_len; /* size of associated buffer */
390 union {
391 caddr_t ifcu_buf;
392 struct ifreq *ifcu_req;
393 } ifc_ifcu;
394 #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
395 #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
396 };
397 .Ed
398 .Pp
399 .Bd -literal
400 /* Structure used in SIOCIFGCLONERS request. */
401 struct if_clonereq {
402 int ifcr_total; /* total cloners (out) */
403 int ifcr_count; /* room for this many in user buffer */
404 char *ifcr_buffer; /* buffer for cloner names */
405 };
406 .Ed
407 .Sh SEE ALSO
408 .Xr ioctl 2 ,
409 .Xr socket 2 ,
410 .Xr intro 4 ,
411 .Xr config 8 ,
412 .Xr routed 8 ,
413 .Xr ifnet 9
414 .Sh HISTORY
415 The
416 .Nm netintro
417 manual appeared in
418 .Bx 4.3 tahoe .