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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 providing
94 a system description to the
97 The DIAGNOSTICS section lists messages which may appear on the console
98 and/or in the system error log,
102 due to errors in device operation.
104 The system currently supports the
106 protocols, the Xerox Network Systems(tm) protocols,
110 Raw socket interfaces are provided to the
118 Consult the appropriate manual pages in this section for more
119 information regarding the support for each protocol family.
121 Associated with each protocol family is an address
122 format. All network address adhere to a general structure,
123 called a sockaddr, described below.
124 However, each protocol
125 imposes finer and more specific structure, generally renaming
126 the variant, which is discussed in the protocol family manual
127 page alluded to above.
128 .Bd -literal -offset indent
138 contains the total length of the structure,
139 which may exceed 16 bytes.
140 The following address values for
142 are known to the system
143 (and additional formats are defined for possible future implementation):
145 #define AF_UNIX 1 /* local to host (pipes, portals) */
146 #define AF_INET 2 /* internetwork: UDP, TCP, etc. */
147 #define AF_CCITT 10 /* CCITT protocols, X.25 etc */
148 #define AF_HYLINK 15 /* NSC Hyperchannel */
152 provides some packet routing facilities.
153 The kernel maintains a routing information database, which
154 is used in selecting the appropriate network interface when
155 transmitting packets.
157 A user process (or possibly multiple co-operating processes)
158 maintains this database by sending messages over a special kind
160 This supplants fixed size
162 used in earlier releases.
164 This facility is described in
167 Each network interface in a system corresponds to a
168 path through which messages may be sent and received. A network
169 interface usually has a hardware device associated with it, though
170 certain interfaces such as the loopback interface,
176 calls may be used to manipulate network interfaces.
179 is made on a socket (typically of type
181 in the desired domain.
182 Most of the requests supported in earlier releases
185 structure as its parameter. This structure has the form
189 char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */
191 struct sockaddr ifru_addr;
192 struct sockaddr ifru_dstaddr;
193 struct sockaddr ifru_broadaddr;
200 #define ifr_addr ifr_ifru.ifru_addr /* address */
201 #define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
202 #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
203 #define ifr_flags ifr_ifru.ifru_flags[0] /* flags (low 16 bits) */
204 #define ifr_flagshigh ifr_ifru.ifru_flags[1] /* flags (high 16 bits) */
205 #define ifr_metric ifr_ifru.ifru_metric /* metric */
206 #define ifr_mtu ifr_ifru.ifru_mtu /* mtu */
207 #define ifr_phys ifr_ifru.ifru_phys /* physical wire */
208 #define ifr_data ifr_ifru.ifru_data /* for use by interface */
212 Calls which are now deprecated are:
213 .Bl -tag -width ".Dv SIOCGIFBRDADDR"
215 Set interface address for protocol family. Following the address
216 assignment, the ``initialization'' routine for
217 the interface is called.
218 .It Dv SIOCSIFDSTADDR
219 Set point to point address for protocol family and interface.
220 .It Dv SIOCSIFBRDADDR
221 Set broadcast address for protocol family and interface.
225 requests to obtain addresses and requests both to set and
226 retrieve other data are still fully supported
230 .Bl -tag -width ".Dv SIOCGIFBRDADDR"
232 Get interface address for protocol family.
233 .It Dv SIOCGIFDSTADDR
234 Get point to point address for protocol family and interface.
235 .It Dv SIOCGIFBRDADDR
236 Get broadcast address for protocol family and interface.
238 Set interface flags field. If the interface is marked down,
239 any processes currently routing packets through the interface
241 some interfaces may be reset so that incoming packets are no longer received.
242 When marked up again, the interface is reinitialized.
246 Set interface routing metric.
247 The metric is used only by user-level routers.
249 Get interface metric.
251 Attempt to create the specified interface.
252 If the interface name is given without a unit number the system
253 will attempt to create a new interface with an arbitrary unit number.
254 On successful return the
256 field will contain the new interface name.
258 Attempt to destroy the specified interface.
261 There are two requests that make use of a new structure:
262 .Bl -tag -width ".Dv SIOCGIFBRDADDR"
264 An interface may have more than one address associated with it
265 in some protocols. This request provides a means to
266 add additional addresses (or modify characteristics of the
267 primary address if the default address for the address family
268 is specified). Rather than making separate calls to
269 set destination or broadcast addresses, or network masks
270 (now an integral feature of multiple protocols)
271 a separate structure is used to specify all three facets simultaneously
273 One would use a slightly tailored version of this struct specific
274 to each family (replacing each sockaddr by one
275 of the family-specific type).
276 Where the sockaddr itself is larger than the
277 default size, one needs to modify the
279 identifier itself to include the total size, as described in
282 This requests deletes the specified address from the list
283 associated with an interface. It also uses the
285 structure to allow for the possibility of protocols allowing
286 multiple masks or destination addresses, and also adopts the
287 convention that specification of the default address means
288 to delete the first address for the interface belonging to
289 the address family in which the original socket was opened.
291 Get interface configuration list. This request takes an
293 structure (see below) as a value-result parameter. The
295 field should be initially set to the size of the buffer
298 On return it will contain the length, in bytes, of the
300 .It Dv SIOCIFGCLONERS
301 Get list of clonable interfaces.
302 This request takes an
304 structure (see below) as a value-result parameter.
307 field should be set to the number of
309 sized strings that can be fit in the buffer pointed to by
313 will be set to the number of clonable interfaces and the buffer pointed
316 will be filled with the names of clonable interfaces aligned on
322 * Structure used in SIOCAIFCONF request.
325 char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */
326 struct sockaddr ifra_addr;
327 struct sockaddr ifra_broadaddr;
328 struct sockaddr ifra_mask;
333 * Structure used in SIOCGIFCONF request.
334 * Used to retrieve interface configuration
335 * for machine (useful for programs which
336 * must know all networks accessible).
339 int ifc_len; /* size of associated buffer */
342 struct ifreq *ifcu_req;
344 #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
345 #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
349 /* Structure used in SIOCIFGCLONERS request. */
351 int ifcr_total; /* total cloners (out) */
352 int ifcr_count; /* room for this many in user buffer */
353 char *ifcr_buffer; /* buffer for cloner names */