bsd/man/man4/netintro.4

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  34 .\"     @(#)netintro.4  8.2 (Berkeley) 11/30/93
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  36 .Dd November 30, 1993
  37 .Dt NETINTRO 4
  38 .Os BSD 4.2
  39 .Sh NAME
  40 .Nm networking
  41 .Nd introduction to networking facilities
  42 .Sh SYNOPSIS
  43 .Fd #include <sys/socket.h>
  44 .Fd #include <net/route.h>
  45 .Fd #include <net/if.h>
  46 .Sh DESCRIPTION
  47 This section is a general introduction to the networking facilities
  48 available in the system.
  49 Documentation in this part of section
  50 4 is broken up into three areas:
  51 .Em protocol families
  52 (domains),
  53 .Em protocols ,
  54 and
  55 .Em network interfaces .
  56 .Pp
  57 All network protocols are associated with a specific
  58 .Em protocol family .
  59 A protocol family provides basic services to the protocol
  60 implementation to allow it to function within a specific
  61 network environment.  These services may include
  62 packet fragmentation and reassembly, routing, addressing, and
  63 basic transport.  A protocol family may support multiple
  64 methods of addressing, though the current protocol implementations
  65 do not.  A protocol family is normally comprised of a number
  66 of protocols, one per
  67 .Xr socket 2
  68 type.  It is not required that a protocol family support
  69 all socket types.  A protocol family may contain multiple
  70 protocols supporting the same socket abstraction.
  71 .Pp
  72 A protocol supports one of the socket abstractions detailed in
  73 .Xr socket 2 .
  74 A specific protocol may be accessed either by creating a
  75 socket of the appropriate type and protocol family, or
  76 by requesting the protocol explicitly when creating a socket.
  77 Protocols normally accept only one type of address format,
  78 usually determined by the addressing structure inherent in
  79 the design of the protocol family/network architecture.
  80 Certain semantics of the basic socket abstractions are
  81 protocol specific.  All protocols are expected to support
  82 the basic model for their particular socket type, but may,
  83 in addition, provide non-standard facilities or extensions
  84 to a mechanism.  For example, a protocol supporting the
  85 .Dv SOCK_STREAM
  86 abstraction may allow more than one byte of out-of-band
  87 data to be transmitted per out-of-band message.
  88 .Pp
  89 A network interface is similar to a device interface.
  90 Network interfaces comprise the lowest layer of the
  91 networking subsystem, interacting with the actual transport
  92 hardware.  An interface may support one or more protocol
  93 families and/or address formats.
  94 The SYNOPSIS section of each network interface
  95 entry gives a sample specification
  96 of the related drivers for use in providing
  97 a system description to the
  98 .Xr config 8
  99 program.
 100 The DIAGNOSTICS section lists messages which may appear on the console
 101 and/or in the system error log,
 102 .Pa /var/log/messages
 103 (see
 104 .Xr syslogd 8 ) ,
 105 due to errors in device operation.
 106 .Sh PROTOCOLS
 107 The system currently supports the
 108 Internet
 109 protocols, the Xerox Network Systems(tm) protocols,
 110 and some of the
 111 .Tn ISO OSI
 112 protocols.
 113 Raw socket interfaces are provided to the
 114 .Tn IP
 115 protocol
 116 layer of the
 117 Internet, and to the
 118 .Tn IDP
 119 protocol of Xerox
 120 .Tn NS .
 121 Consult the appropriate manual pages in this section for more
 122 information regarding the support for each protocol family.
 123 .Sh ADDRESSING
 124 Associated with each protocol family is an address
 125 format.  All network address adhere to a general structure,
 126 called a sockaddr, described below. However, each protocol
 127 imposes finer and more specific structure, generally renaming
 128 the variant, which is discussed in the protocol family manual
 129 page alluded to above.
 130 .Bd -literal -offset indent
 131     struct sockaddr {
 132         u_char  sa_len;
 133         u_char  sa_family;
 134         char    sa_data[14];
 135 };
 136 .Ed
 137 .Pp
 138 The field
 139 .Ar sa_len
 140 contains the total length of the structure,
 141 which may exceed 16 bytes.
 142 The following address values for
 143 .Ar sa_family
 144 are known to the system
 145 (and additional formats are defined for possible future implementation):
 146 .Bd -literal
 147 #define    AF_UNIX      1    /* local to host (pipes) */
 148 #define    AF_INET      2    /* IPv4: UDP, TCP, etc. */
 149 #define    AF_INET6     30   /* IPv6: UDP, TCP, etc. */
 150 #define    AF_NS        6    /* Xerox NS protocols */
 151 #define    AF_CCITT     10   /* CCITT protocols, X.25 etc */
 152 #define    AF_HYLINK    15   /* NSC Hyperchannel */
 153 #define    AF_ISO       18   /* ISO protocols */
 154 #define    AF_VSOCK     40   /* VM Sockets */
 155 .Ed
 156 .Sh ROUTING
 157 Mac OS X provides some packet routing facilities.
 158 The kernel maintains a routing information database, which
 159 is used in selecting the appropriate network interface when
 160 transmitting packets.
 161 .Pp
 162 A user process (or possibly multiple co-operating processes)
 163 maintains this database by sending messages over a special kind
 164 of socket.
 165 This supplants fixed size
 166 .Xr ioctl 2
 167 used in earlier releases.
 168 .Pp
 169 This facility is described in
 170 .Xr route 4 .
 171 .Sh INTERFACES
 172 Each network interface in a system corresponds to a
 173 path through which messages may be sent and received.  A network
 174 interface usually has a hardware device associated with it, though
 175 certain interfaces such as the loopback interface,
 176 .Xr lo 4 ,
 177 do not.
 178 .Pp
 179 The following
 180 .Xr ioctl
 181 calls may be used to manipulate network interfaces.
 182 The
 183 .Xr ioctl
 184 is made on a socket (typically of type
 185 .Dv SOCK_DGRAM )
 186 in the desired domain.
 187 Most of the requests supported in earlier releases
 188 take an
 189 .Ar ifreq
 190 structure as its parameter.  This structure has the form
 191 .Bd -literal
 192 struct  ifreq {
 193 #define    IFNAMSIZ    16
 194     char    ifr_name[IFNAMSIZ];         /* if name, e.g. "en0" */
 195     union {
 196         struct    sockaddr ifru_addr;
 197         struct    sockaddr ifru_dstaddr;
 198         struct    sockaddr ifru_broadaddr;
 199         short     ifru_flags;
 200         int       ifru_metric;
 201         caddr_t   ifru_data;
 202     } ifr_ifru;
 203 #define ifr_addr      ifr_ifru.ifru_addr    /* address */
 204 #define ifr_dstaddr   ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
 205 #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
 206 #define ifr_flags     ifr_ifru.ifru_flags   /* flags */
 207 #define ifr_metric    ifr_ifru.ifru_metric  /* metric */
 208 #define ifr_data      ifr_ifru.ifru_data    /* for use by interface */
 209 };
 210 .Ed
 211 .Pp
 212 Calls which are now deprecated are:
 213 .Bl -tag -width SIOCGIFBRDADDR
 214 .It Dv SIOCSIFADDR
 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.
 222 .El
 223 .Pp
 224 .Xr Ioctl
 225 requests to obtain addresses and requests both to set and
 226 retrieve other data are still fully supported
 227 and use the
 228 .Ar ifreq
 229 structure:
 230 .Bl -tag -width SIOCGIFBRDADDR
 231 .It Dv SIOCGIFADDR
 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.
 237 .It Dv SIOCSIFFLAGS
 238 Set interface flags field.  If the interface is marked down,
 239 any processes currently routing packets through the interface
 240 are notified;
 241 some interfaces may be reset so that incoming packets are no longer received.
 242 When marked up again, the interface is reinitialized.
 243 .It Dv SIOCGIFFLAGS
 244 Get interface flags.
 245 .It Dv SIOCSIFMETRIC
 246 Set interface routing metric.
 247 The metric is used only by user-level routers.
 248 .It Dv SIOCGIFMETRIC
 249 Get interface metric.
 250 .El
 251 .Pp
 252 There are requests that make use of a different structure:
 253 .Bl -tag -width SIOCGIFBRDADDR
 254 .It Dv SIOCAIFADDR
 255 An interface may have more than one address associated with it
 256 in some protocols.  This request provides a means to
 257 add additional addresses (or modify characteristics of the
 258 primary address if the default address for the address family
 259 is specified).  Rather than making separate calls to
 260 set destination or broadcast addresses, or network masks
 261 (now an integral feature of multiple protocols)
 262 a separate structure is used to specify all three facets simultaneously
 263 (see below).
 264 One would use a slightly tailored version of this struct specific
 265 to each family (replacing each sockaddr by one
 266 of the family-specific type).
 267 Where the sockaddr itself is larger than the
 268 default size, one needs to modify the
 269 .Xr ioctl
 270 identifier itself to include the total size, as described in
 271 .Xr ioctl .
 272 .It Dv SIOCDIFADDR
 273 This requests deletes the specified address from the list
 274 associated with an interface.  It  uses the
 275 .Ar ifreq
 276 structure for protocols like
 277 .Dv PF_INET
 278 whose
 279 address fit in the
 280 .Ar sockaddr
 281 structure.
 282 Protocols like
 283 .Dv PF_INET6
 284 with addresses that do not fit in the
 285 .Ar sockaddr
 286 structure
 287 must have a variant of that request.
 288 .It Dv SIOCGIFCONF
 289 Get interface configuration list.  This request takes an
 290 .Ar ifconf
 291 structure (see below) as a value-result parameter.  The
 292 .Ar ifc_len
 293 field should be initially set to the size of the buffer
 294 pointed to by
 295 .Ar ifc_buf .
 296 On return it will contain the length, in bytes, of the
 297 configuration list.
 298 .El
 299 .Bd -literal
 300 /*
 301 * Structure used in SIOCAIFADDR request.
 302 */
 303 struct ifaliasreq {
 304         char    ifra_name[IFNAMSIZ];   /* if name, e.g. "en0" */
 305         struct  sockaddr        ifra_addr;
 306         struct  sockaddr        ifra_broadaddr;
 307         struct  sockaddr        ifra_mask;
 308 };
 309 .Ed
 310 .Pp
 311 .Bd -literal
 312 /*
 313 * Structure used in SIOCGIFCONF request.
 314 * Used to retrieve interface configuration
 315 * for machine (useful for programs which
 316 * must know all networks accessible).
 317 */
 318 struct ifconf {
 319     int   ifc_len;              /* size of associated buffer */
 320     union {
 321         caddr_t    ifcu_buf;
 322         struct     ifreq *ifcu_req;
 323     } ifc_ifcu;
 324 #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
 325 #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
 326 };
 327 .Ed
 328 .Sh SEE ALSO
 329 .Xr ioctl 2 ,
 330 .Xr socket 2 ,
 331 .Xr intro 4 ,
 332 .Xr config 5 ,
 333 .Xr routed 8
 334 .Sh HISTORY
 335 The
 336 .Nm netintro
 337 manual appeared in
 338 .Bx 4.3 tahoe .