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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 */
234 Calls which are now deprecated are:
235 .Bl -tag -width SIOCGIFBRDADDR
237 Set interface address for protocol family.
238 Following the address assignment, the
240 routine for the interface is called.
241 .It Dv SIOCSIFDSTADDR
242 Set point to point address for protocol family and interface.
243 .It Dv SIOCSIFBRDADDR
244 Set broadcast address for protocol family and interface.
248 requests to obtain addresses and requests both to set and
249 retrieve other data are still fully supported
253 .Bl -tag -width SIOCGIFBRDADDR
255 Get interface address for protocol family.
256 .It Dv SIOCGIFDSTADDR
257 Get point to point address for protocol family and interface.
258 .It Dv SIOCGIFBRDADDR
259 Get broadcast address for protocol family and interface.
261 Attempt to set the enabled capabilities field for the interface
267 Note that, depending on the particular interface features,
268 some capabilities may appear hard-coded to enabled, or toggling
269 a capability may affect the status of other ones.
270 The supported capabilities field is read-only, and the
272 field is unused by this call.
274 Get the interface capabilities fields.
275 The values for supported and enabled capabilities will be returned in the
281 structure, respectively.
283 Get the interface description, returned in the
288 The user supplied buffer length should be defined in the
292 struct passed in as parameter, and the length would include
293 the terminating nul character.
294 If there is not enough space to hold the interface length,
295 no copy would be done and the
299 would be set to NULL.
300 The kernel will store the buffer length in the
302 field upon return, regardless whether the buffer itself is
303 sufficient to hold the data.
305 Set the interface description to the value of the
311 field specifying its length (counting the terminating nul).
313 Set interface flags field.
314 If the interface is marked down,
315 any processes currently routing packets through the interface
317 some interfaces may be reset so that incoming packets are no longer received.
318 When marked up again, the interface is reinitialized.
322 Set interface routing metric.
323 The metric is used only by user-level routers.
325 Get interface metric.
327 Attempt to create the specified interface.
328 If the interface name is given without a unit number the system
329 will attempt to create a new interface with an arbitrary unit number.
330 On successful return the
332 field will contain the new interface name.
334 Attempt to destroy the specified interface.
337 There are two requests that make use of a new structure:
338 .Bl -tag -width SIOCGIFBRDADDR
340 An interface may have more than one address associated with it
342 This request provides a means to
343 add additional addresses (or modify characteristics of the
344 primary address if the default address for the address family
346 Rather than making separate calls to
347 set destination or broadcast addresses, or network masks
348 (now an integral feature of multiple protocols)
349 a separate structure is used to specify all three facets simultaneously
351 One would use a slightly tailored version of this struct specific
352 to each family (replacing each sockaddr by one
353 of the family-specific type).
354 Where the sockaddr itself is larger than the
355 default size, one needs to modify the
357 identifier itself to include the total size, as described in
360 This requests deletes the specified address from the list
361 associated with an interface.
364 structure to allow for the possibility of protocols allowing
365 multiple masks or destination addresses, and also adopts the
366 convention that specification of the default address means
367 to delete the first address for the interface belonging to
368 the address family in which the original socket was opened.
370 Get interface configuration list.
371 This request takes an
373 structure (see below) as a value-result parameter.
376 field should be initially set to the size of the buffer
379 On return it will contain the length, in bytes, of the
381 .It Dv SIOCIFGCLONERS
382 Get list of clonable interfaces.
383 This request takes an
385 structure (see below) as a value-result parameter.
388 field should be set to the number of
390 sized strings that can be fit in the buffer pointed to by
394 will be set to the number of clonable interfaces and the buffer pointed
397 will be filled with the names of clonable interfaces aligned on
403 * Structure used in SIOCAIFCONF request.
406 char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
407 struct sockaddr ifra_addr;
408 struct sockaddr ifra_broadaddr;
409 struct sockaddr ifra_mask;
414 * Structure used in SIOCGIFCONF request.
415 * Used to retrieve interface configuration
416 * for machine (useful for programs which
417 * must know all networks accessible).
420 int ifc_len; /* size of associated buffer */
423 struct ifreq *ifcu_req;
425 #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
426 #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
430 /* Structure used in SIOCIFGCLONERS request. */
432 int ifcr_total; /* total cloners (out) */
433 int ifcr_count; /* room for this many in user buffer */
434 char *ifcr_buffer; /* buffer for cloner names */
438 /* Structure used in SIOCGIFDESCR and SIOCSIFDESCR requests */
439 struct ifreq_buffer {
440 size_t length; /* length of the buffer */
441 void *buffer; /* pointer to userland space buffer */