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 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    /* internetwork: UDP, TCP, etc. */
 149 #define    AF_NS        6    /* Xerox NS protocols */
 150 #define    AF_CCITT     10   /* CCITT protocols, X.25 etc */
 151 #define    AF_HYLINK    15   /* NSC Hyperchannel */
 152 #define    AF_ISO       18   /* ISO protocols */
 153 .Ed
 154 .Sh ROUTING
 155 Mac OS X provides some packet routing facilities.
 156 The kernel maintains a routing information database, which
 157 is used in selecting the appropriate network interface when
 158 transmitting packets.
 159 .Pp
 160 A user process (or possibly multiple co-operating processes)
 161 maintains this database by sending messages over a special kind
 162 of socket.
 163 This supplants fixed size
 164 .Xr ioctl 2
 165 used in earlier releases.
 166 .Pp
 167 This facility is described in
 168 .Xr route 4 .
 169 .Sh INTERFACES
 170 Each network interface in a system corresponds to a
 171 path through which messages may be sent and received.  A network
 172 interface usually has a hardware device associated with it, though
 173 certain interfaces such as the loopback interface,
 174 .Xr lo 4 ,
 175 do not.
 176 .Pp
 177 The following
 178 .Xr ioctl
 179 calls may be used to manipulate network interfaces.
 180 The
 181 .Xr ioctl
 182 is made on a socket (typically of type
 183 .Dv SOCK_DGRAM )
 184 in the desired domain.
 185 Most of the requests supported in earlier releases
 186 take an
 187 .Ar ifreq
 188 structure as its parameter.  This structure has the form
 189 .Bd -literal
 190 struct  ifreq {
 191 #define    IFNAMSIZ    16
 192     char    ifr_name[IFNAMSIZ];         /* if name, e.g. "en0" */
 193     union {
 194         struct    sockaddr ifru_addr;
 195         struct    sockaddr ifru_dstaddr;
 196         struct    sockaddr ifru_broadaddr;
 197         short     ifru_flags;
 198         int       ifru_metric;
 199         caddr_t   ifru_data;
 200     } ifr_ifru;
 201 #define ifr_addr      ifr_ifru.ifru_addr    /* address */
 202 #define ifr_dstaddr   ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
 203 #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
 204 #define ifr_flags     ifr_ifru.ifru_flags   /* flags */
 205 #define ifr_metric    ifr_ifru.ifru_metric  /* metric */
 206 #define ifr_data      ifr_ifru.ifru_data    /* for use by interface */
 207 };
 208 .Ed
 209 .Pp
 210 Calls which are now deprecated are:
 211 .Bl -tag -width SIOCGIFBRDADDR
 212 .It Dv SIOCSIFADDR
 213 Set interface address for protocol family.  Following the address
 214 assignment, the ``initialization'' routine for
 215 the interface is called.
 216 .It Dv SIOCSIFDSTADDR
 217 Set point to point address for protocol family and interface.
 218 .It Dv SIOCSIFBRDADDR
 219 Set broadcast address for protocol family and interface.
 220 .El
 221 .Pp
 222 .Xr Ioctl
 223 requests to obtain addresses and requests both to set and
 224 retrieve other data are still fully supported
 225 and use the
 226 .Ar ifreq
 227 structure:
 228 .Bl -tag -width SIOCGIFBRDADDR
 229 .It Dv SIOCGIFADDR
 230 Get interface address for protocol family.
 231 .It Dv SIOCGIFDSTADDR
 232 Get point to point address for protocol family and interface.
 233 .It Dv SIOCGIFBRDADDR
 234 Get broadcast address for protocol family and interface.
 235 .It Dv SIOCSIFFLAGS
 236 Set interface flags field.  If the interface is marked down,
 237 any processes currently routing packets through the interface
 238 are notified;
 239 some interfaces may be reset so that incoming packets are no longer received.
 240 When marked up again, the interface is reinitialized.
 241 .It Dv SIOCGIFFLAGS
 242 Get interface flags.
 243 .It Dv SIOCSIFMETRIC
 244 Set interface routing metric.
 245 The metric is used only by user-level routers.
 246 .It Dv SIOCGIFMETRIC
 247 Get interface metric.
 248 .El
 249 .Pp
 250 There are two requests that make use of a new structure:
 251 .Bl -tag -width SIOCGIFBRDADDR
 252 .It Dv SIOCAIFADDR
 253 An interface may have more than one address associated with it
 254 in some protocols.  This request provides a means to
 255 add additional addresses (or modify characteristics of the
 256 primary address if the default address for the address family
 257 is specified).  Rather than making separate calls to
 258 set destination or broadcast addresses, or network masks
 259 (now an integral feature of multiple protocols)
 260 a separate structure is used to specify all three facets simultaneously
 261 (see below).
 262 One would use a slightly tailored version of this struct specific
 263 to each family (replacing each sockaddr by one
 264 of the family-specific type).
 265 Where the sockaddr itself is larger than the
 266 default size, one needs to modify the
 267 .Xr ioctl
 268 identifier itself to include the total size, as described in
 269 .Xr ioctl .
 270 .It Dv SIOCDIFADDR
 271 This requests deletes the specified address from the list
 272 associated with an interface.  It also uses the
 273 .Ar if_aliasreq
 274 structure to allow for the possibility of protocols allowing
 275 multiple masks or destination addresses, and also adopts the
 276 convention that specification of the default address means
 277 to delete the first address for the interface belonging to
 278 the address family in which the original socket was opened.
 279 .It Dv SIOCGIFCONF
 280 Get interface configuration list.  This request takes an
 281 .Ar ifconf
 282 structure (see below) as a value-result parameter.  The
 283 .Ar ifc_len
 284 field should be initially set to the size of the buffer
 285 pointed to by
 286 .Ar ifc_buf .
 287 On return it will contain the length, in bytes, of the
 288 configuration list.
 289 .El
 290 .Bd -literal
 291 /*
 292 * Structure used in SIOCAIFADDR request.
 293 */
 294 struct ifaliasreq {
 295         char    ifra_name[IFNAMSIZ];   /* if name, e.g. "en0" */
 296         struct  sockaddr        ifra_addr;
 297         struct  sockaddr        ifra_broadaddr;
 298         struct  sockaddr        ifra_mask;
 299 };
 300 .Ed
 301 .Pp
 302 .Bd -literal
 303 /*
 304 * Structure used in SIOCGIFCONF request.
 305 * Used to retrieve interface configuration
 306 * for machine (useful for programs which
 307 * must know all networks accessible).
 308 */
 309 struct ifconf {
 310     int   ifc_len;              /* size of associated buffer */
 311     union {
 312         caddr_t    ifcu_buf;
 313         struct     ifreq *ifcu_req;
 314     } ifc_ifcu;
 315 #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
 316 #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */
 317 };
 318 .Ed
 319 .Sh SEE ALSO
 320 .Xr socket 2 ,
 321 .Xr ioctl 2 ,
 322 .Xr intro 4 ,
 323 .Xr config 8 ,
 324 .Xr routed 8
 325 .Sh HISTORY
 326 The
 327 .Nm netintro
 328 manual appeared in
 329 .Bx 4.3 tahoe .