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32 .\" @(#)netintro.4 8.2 (Berkeley) 11/30/93
40 .Nd introduction to networking facilities
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:
56 .Em network interfaces .
58 All network protocols are associated with a specific
60 A protocol family provides basic services to the protocol
61 implementation to allow it to function within a specific
63 These services may include
64 packet fragmentation and reassembly, routing, addressing, and
66 A protocol family may support multiple
67 methods of addressing, though the current protocol implementations
69 A protocol family is normally comprised of a number of protocols, one per
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.
76 A protocol supports one of the socket abstractions detailed in
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
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
90 For example, a protocol supporting the
92 abstraction may allow more than one byte of out-of-band
93 data to be transmitted per out-of-band message.
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
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
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
111 due to errors in device operation.
113 The system currently supports the
115 protocols, the Xerox Network Systems(tm) protocols,
119 Raw socket interfaces are provided to the
127 Consult the appropriate manual pages in this section for more
128 information regarding the support for each protocol family.
130 Associated with each protocol family is an address
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
148 contains the total length of the structure,
149 which may exceed 16 bytes.
150 The following address values for
152 are known to the system
153 (and additional formats are defined for possible future implementation):
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 */
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.
169 A user process (or possibly multiple co-operating processes)
170 maintains this database by sending messages over a special kind
172 This supplants fixed size
174 used in earlier releases.
176 This facility is described in
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,
188 calls may be used to manipulate network interfaces.
191 is made on a socket (typically of type
193 in the desired domain.
194 Most of the requests supported in earlier releases
197 structure as its parameter.
198 This structure has the form
202 char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */
204 struct sockaddr ifru_addr;
205 struct sockaddr ifru_dstaddr;
206 struct sockaddr ifru_broadaddr;
207 struct ifreq_buffer ifru_buffer;
217 #define ifr_addr ifr_ifru.ifru_addr /* address */
218 #define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
219 #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
220 #define ifr_buffer ifr_ifru.ifru_buffer /* user supplied buffer with its length */
221 #define ifr_flags ifr_ifru.ifru_flags[0] /* flags (low 16 bits) */
222 #define ifr_flagshigh ifr_ifru.ifru_flags[1] /* flags (high 16 bits) */
223 #define ifr_metric ifr_ifru.ifru_metric /* metric */
224 #define ifr_mtu ifr_ifru.ifru_mtu /* mtu */
225 #define ifr_phys ifr_ifru.ifru_phys /* physical wire */
226 #define ifr_media ifr_ifru.ifru_media /* physical media */
227 #define ifr_data ifr_ifru.ifru_data /* for use by interface */
228 #define ifr_reqcap ifr_ifru.ifru_cap[0] /* requested capabilities */
229 #define ifr_curcap ifr_ifru.ifru_cap[1] /* current capabilities */
230 #define ifr_index ifr_ifru.ifru_index /* interface index */
235 requests to obtain addresses and requests both to set and
236 retrieve other data are still fully supported
240 .Bl -tag -width SIOCGIFBRDADDR
242 Get interface address for protocol family.
243 .It Dv SIOCGIFDSTADDR
244 Get point to point address for protocol family and interface.
245 .It Dv SIOCGIFBRDADDR
246 Get broadcast address for protocol family and interface.
248 Attempt to set the enabled capabilities field for the interface
254 Note that, depending on the particular interface features,
255 some capabilities may appear hard-coded to enabled, or toggling
256 a capability may affect the status of other ones.
257 The supported capabilities field is read-only, and the
259 field is unused by this call.
261 Get the interface capabilities fields.
262 The values for supported and enabled capabilities will be returned in the
268 structure, respectively.
270 Get the interface description, returned in the
275 The user supplied buffer length should be defined in the
279 struct passed in as parameter, and the length would include
280 the terminating nul character.
281 If there is not enough space to hold the interface length,
282 no copy would be done and the
286 would be set to NULL.
287 The kernel will store the buffer length in the
289 field upon return, regardless whether the buffer itself is
290 sufficient to hold the data.
292 Set the interface description to the value of the
298 field specifying its length (counting the terminating nul).
300 Set interface flags field.
301 If the interface is marked down,
302 any processes currently routing packets through the interface
304 some interfaces may be reset so that incoming packets are no longer received.
305 When marked up again, the interface is reinitialized.
309 Set interface routing metric.
310 The metric is used only by user-level routers.
312 Get interface metric.
314 Attempt to create the specified interface.
315 If the interface name is given without a unit number the system
316 will attempt to create a new interface with an arbitrary unit number.
317 On successful return the
319 field will contain the new interface name.
321 Attempt to destroy the specified interface.
324 There are two requests that make use of a new structure:
325 .Bl -tag -width SIOCGIFBRDADDR
327 An interface may have more than one address associated with it
329 This request provides a means to
330 add additional addresses (or modify characteristics of the
331 primary address if the default address for the address family
333 Rather than making separate calls to
334 set destination or broadcast addresses, or network masks
335 (now an integral feature of multiple protocols)
336 a separate structure is used to specify all three facets simultaneously
338 One would use a slightly tailored version of this struct specific
339 to each family (replacing each sockaddr by one
340 of the family-specific type).
341 Where the sockaddr itself is larger than the
342 default size, one needs to modify the
344 identifier itself to include the total size, as described in
347 This requests deletes the specified address from the list
348 associated with an interface.
351 structure to allow for the possibility of protocols allowing
352 multiple masks or destination addresses, and also adopts the
353 convention that specification of the default address means
354 to delete the first address for the interface belonging to
355 the address family in which the original socket was opened.
357 Get interface configuration list.
358 This request takes an
360 structure (see below) as a value-result parameter.
363 field should be initially set to the size of the buffer
366 On return it will contain the length, in bytes, of the
368 .It Dv SIOCIFGCLONERS
369 Get list of clonable interfaces.
370 This request takes an
372 structure (see below) as a value-result parameter.
375 field should be set to the number of
377 sized strings that can be fit in the buffer pointed to by
381 will be set to the number of clonable interfaces and the buffer pointed
384 will be filled with the names of clonable interfaces aligned on
390 * Structure used in SIOCAIFADDR request.
393 char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
394 struct sockaddr ifra_addr;
395 struct sockaddr ifra_broadaddr;
396 struct sockaddr ifra_mask;
401 * Structure used in SIOCGIFCONF request.
402 * Used to retrieve interface configuration
403 * for machine (useful for programs which
404 * must know all networks accessible).
407 int ifc_len; /* size of associated buffer */
410 struct ifreq *ifcu_req;
412 #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
413 #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
417 /* Structure used in SIOCIFGCLONERS request. */
419 int ifcr_total; /* total cloners (out) */
420 int ifcr_count; /* room for this many in user buffer */
421 char *ifcr_buffer; /* buffer for cloner names */
425 /* Structure used in SIOCGIFDESCR and SIOCSIFDESCR requests */
426 struct ifreq_buffer {
427 size_t length; /* length of the buffer */
428 void *buffer; /* pointer to userland space buffer */