bsd/man/man4/netintro.4

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  34 .\"     @(#)netintro.4  8.2 (Berkeley) 11/30/93
  35 .\"
  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 .Ed
 155 .Sh ROUTING
 156 Mac OS X provides some packet routing facilities.
 157 The kernel maintains a routing information database, which
 158 is used in selecting the appropriate network interface when
 159 transmitting packets.
 160 .Pp
 161 A user process (or possibly multiple co-operating processes)
 162 maintains this database by sending messages over a special kind
 163 of socket.
 164 This supplants fixed size
 165 .Xr ioctl 2
 166 used in earlier releases.
 167 .Pp
 168 This facility is described in
 169 .Xr route 4 .
 170 .Sh INTERFACES
 171 Each network interface in a system corresponds to a
 172 path through which messages may be sent and received.  A network
 173 interface usually has a hardware device associated with it, though
 174 certain interfaces such as the loopback interface,
 175 .Xr lo 4 ,
 176 do not.
 177 .Pp
 178 The following
 179 .Xr ioctl
 180 calls may be used to manipulate network interfaces.
 181 The
 182 .Xr ioctl
 183 is made on a socket (typically of type
 184 .Dv SOCK_DGRAM )
 185 in the desired domain.
 186 Most of the requests supported in earlier releases
 187 take an
 188 .Ar ifreq
 189 structure as its parameter.  This structure has the form
 190 .Bd -literal
 191 struct  ifreq {
 192 #define    IFNAMSIZ    16
 193     char    ifr_name[IFNAMSIZ];         /* if name, e.g. "en0" */
 194     union {
 195         struct    sockaddr ifru_addr;
 196         struct    sockaddr ifru_dstaddr;
 197         struct    sockaddr ifru_broadaddr;
 198         short     ifru_flags;
 199         int       ifru_metric;
 200         caddr_t   ifru_data;
 201     } ifr_ifru;
 202 #define ifr_addr      ifr_ifru.ifru_addr    /* address */
 203 #define ifr_dstaddr   ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
 204 #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
 205 #define ifr_flags     ifr_ifru.ifru_flags   /* flags */
 206 #define ifr_metric    ifr_ifru.ifru_metric  /* metric */
 207 #define ifr_data      ifr_ifru.ifru_data    /* for use by interface */
 208 };
 209 .Ed
 210 .Pp
 211 Calls which are now deprecated are:
 212 .Bl -tag -width SIOCGIFBRDADDR
 213 .It Dv SIOCSIFADDR
 214 Set interface address for protocol family.  Following the address
 215 assignment, the ``initialization'' routine for
 216 the interface is called.
 217 .It Dv SIOCSIFDSTADDR
 218 Set point to point address for protocol family and interface.
 219 .It Dv SIOCSIFBRDADDR
 220 Set broadcast address for protocol family and interface.
 221 .El
 222 .Pp
 223 .Xr Ioctl
 224 requests to obtain addresses and requests both to set and
 225 retrieve other data are still fully supported
 226 and use the
 227 .Ar ifreq
 228 structure:
 229 .Bl -tag -width SIOCGIFBRDADDR
 230 .It Dv SIOCGIFADDR
 231 Get interface address for protocol family.
 232 .It Dv SIOCGIFDSTADDR
 233 Get point to point address for protocol family and interface.
 234 .It Dv SIOCGIFBRDADDR
 235 Get broadcast address for protocol family and interface.
 236 .It Dv SIOCSIFFLAGS
 237 Set interface flags field.  If the interface is marked down,
 238 any processes currently routing packets through the interface
 239 are notified;
 240 some interfaces may be reset so that incoming packets are no longer received.
 241 When marked up again, the interface is reinitialized.
 242 .It Dv SIOCGIFFLAGS
 243 Get interface flags.
 244 .It Dv SIOCSIFMETRIC
 245 Set interface routing metric.
 246 The metric is used only by user-level routers.
 247 .It Dv SIOCGIFMETRIC
 248 Get interface metric.
 249 .El
 250 .Pp
 251 There are two requests that make use of a new structure:
 252 .Bl -tag -width SIOCGIFBRDADDR
 253 .It Dv SIOCAIFADDR
 254 An interface may have more than one address associated with it
 255 in some protocols.  This request provides a means to
 256 add additional addresses (or modify characteristics of the
 257 primary address if the default address for the address family
 258 is specified).  Rather than making separate calls to
 259 set destination or broadcast addresses, or network masks
 260 (now an integral feature of multiple protocols)
 261 a separate structure is used to specify all three facets simultaneously
 262 (see below).
 263 One would use a slightly tailored version of this struct specific
 264 to each family (replacing each sockaddr by one
 265 of the family-specific type).
 266 Where the sockaddr itself is larger than the
 267 default size, one needs to modify the
 268 .Xr ioctl
 269 identifier itself to include the total size, as described in
 270 .Xr ioctl .
 271 .It Dv SIOCDIFADDR
 272 This requests deletes the specified address from the list
 273 associated with an interface.  It also uses the
 274 .Ar if_aliasreq
 275 structure to allow for the possibility of protocols allowing
 276 multiple masks or destination addresses, and also adopts the
 277 convention that specification of the default address means
 278 to delete the first address for the interface belonging to
 279 the address family in which the original socket was opened.
 280 .It Dv SIOCGIFCONF
 281 Get interface configuration list.  This request takes an
 282 .Ar ifconf
 283 structure (see below) as a value-result parameter.  The
 284 .Ar ifc_len
 285 field should be initially set to the size of the buffer
 286 pointed to by
 287 .Ar ifc_buf .
 288 On return it will contain the length, in bytes, of the
 289 configuration list.
 290 .El
 291 .Bd -literal
 292 /*
 293 * Structure used in SIOCAIFADDR request.
 294 */
 295 struct ifaliasreq {
 296         char    ifra_name[IFNAMSIZ];   /* if name, e.g. "en0" */
 297         struct  sockaddr        ifra_addr;
 298         struct  sockaddr        ifra_broadaddr;
 299         struct  sockaddr        ifra_mask;
 300 };
 301 .Ed
 302 .Pp
 303 .Bd -literal
 304 /*
 305 * Structure used in SIOCGIFCONF request.
 306 * Used to retrieve interface configuration
 307 * for machine (useful for programs which
 308 * must know all networks accessible).
 309 */
 310 struct ifconf {
 311     int   ifc_len;              /* size of associated buffer */
 312     union {
 313         caddr_t    ifcu_buf;
 314         struct     ifreq *ifcu_req;
 315     } ifc_ifcu;
 316 #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
 317 #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
 318 };
 319 .Ed
 320 .Sh SEE ALSO
 321 .Xr ioctl 2 ,
 322 .Xr socket 2 ,
 323 .Xr intro 4 ,
 324 .Xr config 5 ,
 325 .Xr routed 8
 326 .Sh HISTORY
 327 The
 328 .Nm netintro
 329 manual appeared in
 330 .Bx 4.3 tahoe .