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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 $
36 .Nd introduction to networking facilities
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:
52 .Em network interfaces .
54 All network protocols are associated with a specific
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
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.
69 A protocol supports one of the socket abstractions detailed in
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
83 abstraction may allow more than one byte of out-of-band
84 data to be transmitted per out-of-band message.
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,
99 due to errors in device operation.
101 The system currently supports the
103 protocols, the Xerox Network Systems(tm) protocols,
107 Raw socket interfaces are provided to the
115 Consult the appropriate manual pages in this section for more
116 information regarding the support for each protocol family.
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
135 contains the total length of the structure,
136 which may exceed 16 bytes.
137 The following address values for
139 are known to the system
140 (and additional formats are defined for possible future implementation):
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 */
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.
154 A user process (or possibly multiple co-operating processes)
155 maintains this database by sending messages over a special kind
157 This supplants fixed size
159 used in earlier releases.
161 This facility is described in
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,
173 calls may be used to manipulate network interfaces.
176 is made on a socket (typically of type
178 in the desired domain.
179 Most of the requests supported in earlier releases
182 structure as its parameter. This structure has the form
186 char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */
188 struct sockaddr ifru_addr;
189 struct sockaddr ifru_dstaddr;
190 struct sockaddr ifru_broadaddr;
197 #define ifr_addr ifr_ifru.ifru_addr /* address */
198 #define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
199 #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
200 #define ifr_flags ifr_ifru.ifru_flags[0] /* flags (low 16 bits) */
201 #define ifr_flagshigh ifr_ifru.ifru_flags[1] /* flags (high 16 bits) */
202 #define ifr_metric ifr_ifru.ifru_metric /* metric */
203 #define ifr_mtu ifr_ifru.ifru_mtu /* mtu */
204 #define ifr_phys ifr_ifru.ifru_phys /* physical wire */
205 #define ifr_data ifr_ifru.ifru_data /* for use by interface */
209 Calls which are now deprecated are:
210 .Bl -tag -width ".Dv SIOCGIFBRDADDR"
212 Set interface address for protocol family. Following the address
213 assignment, the ``initialization'' routine for
214 the interface is called.
215 .It Dv SIOCSIFDSTADDR
216 Set point to point address for protocol family and interface.
217 .It Dv SIOCSIFBRDADDR
218 Set broadcast address for protocol family and interface.
222 requests to obtain addresses and requests both to set and
223 retrieve other data are still fully supported
227 .Bl -tag -width ".Dv SIOCGIFBRDADDR"
229 Get interface address for protocol family.
230 .It Dv SIOCGIFDSTADDR
231 Get point to point address for protocol family and interface.
232 .It Dv SIOCGIFBRDADDR
233 Get broadcast address for protocol family and interface.
235 Set interface flags field. If the interface is marked down,
236 any processes currently routing packets through the interface
238 some interfaces may be reset so that incoming packets are no longer received.
239 When marked up again, the interface is reinitialized.
243 Set interface routing metric.
244 The metric is used only by user-level routers.
246 Get interface metric.
248 Attempt to create the specified interface.
249 If the interface name is given without a unit number the system
250 will attempt to create a new interface with an arbitrary unit number.
251 On successful return the
253 field will contain the new interface name.
255 Attempt to destroy the specified interface.
258 There are two requests that make use of a new structure:
259 .Bl -tag -width ".Dv SIOCGIFBRDADDR"
261 An interface may have more than one address associated with it
262 in some protocols. This request provides a means to
263 add additional addresses (or modify characteristics of the
264 primary address if the default address for the address family
265 is specified). Rather than making separate calls to
266 set destination or broadcast addresses, or network masks
267 (now an integral feature of multiple protocols)
268 a separate structure is used to specify all three facets simultaneously
270 One would use a slightly tailored version of this struct specific
271 to each family (replacing each sockaddr by one
272 of the family-specific type).
273 Where the sockaddr itself is larger than the
274 default size, one needs to modify the
276 identifier itself to include the total size, as described in
279 This requests deletes the specified address from the list
280 associated with an interface. It also uses the
282 structure to allow for the possibility of protocols allowing
283 multiple masks or destination addresses, and also adopts the
284 convention that specification of the default address means
285 to delete the first address for the interface belonging to
286 the address family in which the original socket was opened.
288 This request provides means to get additional addresses
289 together with netmask and broadcast/destination from an
295 Get interface configuration list. This request takes an
297 structure (see below) as a value-result parameter. The
299 field should be initially set to the size of the buffer
302 On return it will contain the length, in bytes, of the
304 .It Dv SIOCIFGCLONERS
305 Get list of clonable interfaces.
306 This request takes an
308 structure (see below) as a value-result parameter.
311 field should be set to the number of
313 sized strings that can be fit in the buffer pointed to by
317 will be set to the number of clonable interfaces and the buffer pointed
320 will be filled with the names of clonable interfaces aligned on
326 * Structure used in SIOCAIFCONF request.
329 char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
330 struct sockaddr ifra_addr;
331 struct sockaddr ifra_broadaddr;
332 struct sockaddr ifra_mask;
337 * Structure used in SIOCGIFCONF request.
338 * Used to retrieve interface configuration
339 * for machine (useful for programs which
340 * must know all networks accessible).
343 int ifc_len; /* size of associated buffer */
346 struct ifreq *ifcu_req;
348 #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
349 #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
353 /* Structure used in SIOCIFGCLONERS request. */
355 int ifcr_total; /* total cloners (out) */
356 int ifcr_count; /* room for this many in user buffer */
357 char *ifcr_buffer; /* buffer for cloner names */