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IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 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 $ 30.\" 31.Dd August 8, 2015 32.Dt NETINTRO 4 33.Os 34.Sh NAME 35.Nm networking 36.Nd introduction to networking facilities 37.Sh SYNOPSIS 38.In sys/types.h 39.In sys/time.h 40.In sys/socket.h 41.In net/if.h 42.In net/route.h 43.Sh DESCRIPTION 44This section is a general introduction to the networking facilities 45available in the system. 46Documentation in this part of section 474 is broken up into three areas: 48.Em protocol families 49(domains), 50.Em protocols , 51and 52.Em network interfaces . 53.Pp 54All network protocols are associated with a specific 55.Em protocol family . 56A protocol family provides basic services to the protocol 57implementation to allow it to function within a specific 58network environment. These services may include 59packet fragmentation and reassembly, routing, addressing, and 60basic transport. A protocol family may support multiple 61methods of addressing, though the current protocol implementations 62do not. A protocol family is normally comprised of a number 63of protocols, one per 64.Xr socket 2 65type. It is not required that a protocol family support 66all socket types. A protocol family may contain multiple 67protocols supporting the same socket abstraction. 68.Pp 69A protocol supports one of the socket abstractions detailed in 70.Xr socket 2 . 71A specific protocol may be accessed either by creating a 72socket of the appropriate type and protocol family, or 73by requesting the protocol explicitly when creating a socket. 74Protocols normally accept only one type of address format, 75usually determined by the addressing structure inherent in 76the design of the protocol family/network architecture. 77Certain semantics of the basic socket abstractions are 78protocol specific. All protocols are expected to support 79the basic model for their particular socket type, but may, 80in addition, provide non-standard facilities or extensions 81to a mechanism. For example, a protocol supporting the 82.Dv SOCK_STREAM 83abstraction may allow more than one byte of out-of-band 84data to be transmitted per out-of-band message. 85.Pp 86A network interface is similar to a device interface. 87Network interfaces comprise the lowest layer of the 88networking subsystem, interacting with the actual transport 89hardware. An interface may support one or more protocol 90families and/or address formats. 91The SYNOPSIS section of each network interface 92entry gives a sample specification 93of the related drivers for use in providing 94a system description to the 95.Xr config 8 96program. 97The DIAGNOSTICS section lists messages which may appear on the console 98and/or in the system error log, 99.Pa /var/log/messages 100(see 101.Xr syslogd 8 ) , 102due to errors in device operation. 103.Sh PROTOCOLS 104The system currently supports the 105Internet 106protocols, the Xerox Network Systems(tm) protocols, 107and some of the 108.Tn ISO OSI 109protocols. 110Raw socket interfaces are provided to the 111.Tn IP 112protocol 113layer of the 114Internet, and to the 115.Tn IDP 116protocol of Xerox 117.Tn NS . 118Consult the appropriate manual pages in this section for more 119information regarding the support for each protocol family. 120.Sh ADDRESSING 121Associated with each protocol family is an address 122format. All network address adhere to a general structure, 123called a sockaddr, described below. 124However, each protocol 125imposes finer and more specific structure, generally renaming 126the variant, which is discussed in the protocol family manual 127page alluded to above. 128.Bd -literal -offset indent 129 struct sockaddr { 130 u_char sa_len; 131 u_char sa_family; 132 char sa_data[14]; 133}; 134.Ed 135.Pp 136The field 137.Va sa_len 138contains the total length of the structure, 139which may exceed 16 bytes. 140The following address values for 141.Va sa_family 142are known to the system 143(and additional formats are defined for possible future implementation): 144.Bd -literal 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 */ 149.Ed 150.Sh ROUTING 151.Ux 152provides some packet routing facilities. 153The kernel maintains a routing information database, which 154is used in selecting the appropriate network interface when 155transmitting packets. 156.Pp 157A user process (or possibly multiple co-operating processes) 158maintains this database by sending messages over a special kind 159of socket. 160This supplants fixed size 161.Xr ioctl 2 162used in earlier releases. 163.Pp 164This facility is described in 165.Xr route 4 . 166.Sh INTERFACES 167Each network interface in a system corresponds to a 168path through which messages may be sent and received. A network 169interface usually has a hardware device associated with it, though 170certain interfaces such as the loopback interface, 171.Xr lo 4 , 172do not. 173.Pp 174The following 175.Xr ioctl 2 176calls may be used to manipulate network interfaces. 177The 178.Fn ioctl 179is made on a socket (typically of type 180.Dv SOCK_DGRAM ) 181in the desired domain. 182Most of the requests supported in earlier releases 183take an 184.Vt ifreq 185structure as its parameter. This structure has the form 186.Bd -literal 187struct ifreq { 188#define IFNAMSIZ 16 189 char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 190 union { 191 struct sockaddr ifru_addr; 192 struct sockaddr ifru_dstaddr; 193 struct sockaddr ifru_broadaddr; 194 short ifru_flags[2]; 195 int ifru_metric; 196 int ifru_mtu; 197 int ifru_phys; 198 caddr_t ifru_data; 199 } ifr_ifru; 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 */ 209}; 210.Ed 211.Pp 212Calls which are now deprecated are: 213.Bl -tag -width ".Dv SIOCGIFBRDADDR" 214.It Dv SIOCSIFADDR 215Set interface address for protocol family. Following the address 216assignment, the ``initialization'' routine for 217the interface is called. 218.It Dv SIOCSIFDSTADDR 219Set point to point address for protocol family and interface. 220.It Dv SIOCSIFBRDADDR 221Set broadcast address for protocol family and interface. 222.El 223.Pp 224.Fn Ioctl 225requests to obtain addresses and requests both to set and 226retrieve other data are still fully supported 227and use the 228.Vt ifreq 229structure: 230.Bl -tag -width ".Dv SIOCGIFBRDADDR" 231.It Dv SIOCGIFADDR 232Get interface address for protocol family. 233.It Dv SIOCGIFDSTADDR 234Get point to point address for protocol family and interface. 235.It Dv SIOCGIFBRDADDR 236Get broadcast address for protocol family and interface. 237.It Dv SIOCSIFFLAGS 238Set interface flags field. If the interface is marked down, 239any processes currently routing packets through the interface 240are notified; 241some interfaces may be reset so that incoming packets are no longer received. 242When marked up again, the interface is reinitialized. 243.It Dv SIOCGIFFLAGS 244Get interface flags. 245.It Dv SIOCSIFMETRIC 246Set interface routing metric. 247The metric is used only by user-level routers. 248.It Dv SIOCGIFMETRIC 249Get interface metric. 250.It Dv SIOCIFCREATE 251Attempt to create the specified interface. 252If the interface name is given without a unit number the system 253will attempt to create a new interface with an arbitrary unit number. 254On successful return the 255.Va ifr_name 256field will contain the new interface name. 257.It Dv SIOCIFDESTROY 258Attempt to destroy the specified interface. 259.El 260.Pp 261There are two requests that make use of a new structure: 262.Bl -tag -width ".Dv SIOCGIFBRDADDR" 263.It Dv SIOCAIFADDR 264An interface may have more than one address associated with it 265in some protocols. This request provides a means to 266add additional addresses (or modify characteristics of the 267primary address if the default address for the address family 268is specified). Rather than making separate calls to 269set destination or broadcast addresses, or network masks 270(now an integral feature of multiple protocols) 271a separate structure is used to specify all three facets simultaneously 272(see below). 273One would use a slightly tailored version of this struct specific 274to each family (replacing each sockaddr by one 275of the family-specific type). 276Where the sockaddr itself is larger than the 277default size, one needs to modify the 278.Fn ioctl 279identifier itself to include the total size, as described in 280.Fn ioctl . 281.It Dv SIOCDIFADDR 282This requests deletes the specified address from the list 283associated with an interface. It also uses the 284.Vt ifaliasreq 285structure to allow for the possibility of protocols allowing 286multiple masks or destination addresses, and also adopts the 287convention that specification of the default address means 288to delete the first address for the interface belonging to 289the address family in which the original socket was opened. 290.It Dv SIOCGIFCONF 291Get interface configuration list. This request takes an 292.Vt ifconf 293structure (see below) as a value-result parameter. The 294.Va ifc_len 295field should be initially set to the size of the buffer 296pointed to by 297.Va ifc_buf . 298On return it will contain the length, in bytes, of the 299configuration list. 300.It Dv SIOCIFGCLONERS 301Get list of clonable interfaces. 302This request takes an 303.Vt if_clonereq 304structure (see below) as a value-result parameter. 305The 306.Va ifcr_count 307field should be set to the number of 308.Dv IFNAMSIZ 309sized strings that can be fit in the buffer pointed to by 310.Va ifcr_buffer . 311On return, 312.Va ifcr_total 313will be set to the number of clonable interfaces and the buffer pointed 314to by 315.Va ifcr_buffer 316will be filled with the names of clonable interfaces aligned on 317.Dv IFNAMSIZ 318boundaries. 319.El 320.Bd -literal 321/* 322* Structure used in SIOCAIFCONF request. 323*/ 324struct ifaliasreq { 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; 329}; 330.Ed 331.Bd -literal 332/* 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). 337*/ 338struct ifconf { 339 int ifc_len; /* size of associated buffer */ 340 union { 341 caddr_t ifcu_buf; 342 struct ifreq *ifcu_req; 343 } ifc_ifcu; 344#define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */ 345#define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */ 346}; 347.Ed 348.Bd -literal 349/* Structure used in SIOCIFGCLONERS request. */ 350struct if_clonereq { 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 */ 354}; 355.Ed 356.Sh SEE ALSO 357.Xr ioctl 2 , 358.Xr socket 2 , 359.Xr intro 4 , 360.Xr config 8 , 361.Xr routed 8 362.Sh HISTORY 363The 364.Nm netintro 365manual appeared in 366.Bx 4.3 tahoe . 367