1.\" $NetBSD: netintro.4,v 1.18 2003/08/07 10:31:03 agc Exp $ 2.\" 3.\" Copyright (c) 1983, 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)netintro.4 8.2 (Berkeley) 11/30/93 31.\" 32.Dd August 29, 2000 33.Dt NETINTRO 4 34.Os 35.Sh NAME 36.Nm netintro 37.Nd introduction to networking facilities 38.Sh SYNOPSIS 39.In sys/types.h 40.In sys/socket.h 41.In net/route.h 42.In net/if.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 implementation 57to allow it to function within a specific network environment. 58These services may include packet fragmentation and reassembly, 59routing, addressing, and basic transport. 60A protocol family may support multiple methods of addressing, though 61the current protocol implementations do not. 62A protocol family normally comprises a number of protocols, one per 63.Xr socket 2 64type. 65It is not required that a protocol family support all socket types. 66A protocol family may contain multiple protocols supporting the 67same 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. 79All protocols are expected to support the basic model for their 80particular socket type, but may, in addition, provide non-standard 81facilities or extensions to a mechanism. 82For example, a protocol supporting the 83.Dv SOCK_STREAM 84abstraction may allow more than one byte of out-of-band 85data to be transmitted per out-of-band message. 86.Pp 87A network interface is similar to a device interface. 88Network interfaces comprise the lowest layer of the networking 89subsystem, interacting with the actual transport hardware. 90An interface may support one or more protocol families and/or address formats. 91The 92.Em SYNOPSIS 93section of each network interface entry gives a sample specification 94of the related drivers for use in providing a system description to the 95.Xr config 8 96program. 97.Pp 98The 99.Em DIAGNOSTICS 100section lists messages which may appear on the console 101and/or in the system error log, 102.Pa /var/log/messages 103(see 104.Xr syslogd 8 ) , 105due to errors in device operation. 106.Sh PROTOCOLS 107The system currently supports the Internet protocols, 108the Xerox Network Systems (XNS)(tm) protocols, and some of the 109.Tn ISO OSI 110protocols. 111Raw socket interfaces are provided to the 112.Tn IP 113protocol layer of the Internet, and to the 114.Tn IDP 115protocol of Xerox 116.Tn NS . 117Consult the appropriate manual pages in this section for more 118information regarding the support for each protocol family. 119.Sh ADDRESSING 120Associated with each protocol family is an address format. 121All network address adhere to a general structure, called a sockaddr, 122described below. 123However, each protocol imposes finer and more specific structure, 124generally renaming the variant, which is discussed in the protocol 125family manual page alluded to above. 126.Bd -literal -offset indent 127struct sockaddr { 128 u_char sa_len; 129 u_char sa_family; 130 char sa_data[14]; 131}; 132.Ed 133.Pp 134The field 135.Ar sa_len 136contains the total length of the of the structure, which may exceed 16 bytes. 137The following address values for 138.Ar sa_family 139are known to the system 140(and additional formats are defined for possible future implementation): 141.Bd -literal 142#define AF_LOCAL 1 /* local to host (pipes, portals) */ 143#define AF_INET 2 /* internetwork: UDP, TCP, etc. */ 144#define AF_NS 6 /* Xerox NS protocols */ 145#define AF_CCITT 10 /* CCITT protocols, X.25 etc */ 146#define AF_HYLINK 15 /* NSC Hyperchannel */ 147#define AF_ISO 18 /* ISO protocols */ 148.Ed 149.Sh ROUTING 150.Ux 151provides some packet routing facilities. 152The kernel maintains a routing information database, which 153is used in selecting the appropriate network interface when 154transmitting packets. 155.Pp 156A user process (or possibly multiple co-operating processes) 157maintains this database by sending messages over a special kind 158of socket. 159This supplants fixed size 160.Xr ioctl 2 161used in earlier releases. 162.Pp 163This facility is described in 164.Xr route 4 . 165.Sh INTERFACES 166Each network interface in a system corresponds to a 167path through which messages may be sent and received. 168A network interface usually has a hardware device associated with it, 169though certain interfaces such as the loopback interface, 170.Xr lo 4 , 171do not. 172.Pp 173The following 174.Xr ioctl 2 175calls may be used to manipulate network interfaces. 176The 177.Xr ioctl 2 178is made on a socket (typically of type 179.Dv SOCK_DGRAM ) 180in the desired domain. 181Most of the requests supported in earlier releases 182take an 183.Ar ifreq 184structure as its parameter. 185This 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; 195 int ifru_metric; 196 caddr_t ifru_data; 197 } ifr_ifru; 198#define ifr_addr ifr_ifru.ifru_addr /* address */ 199#define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */ 200#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */ 201#define ifr_flags ifr_ifru.ifru_flags /* flags */ 202#define ifr_metric ifr_ifru.ifru_metric /* metric */ 203#define ifr_data ifr_ifru.ifru_data /* for use by interface */ 204}; 205.Ed 206.Pp 207Calls which are now deprecated are: 208.Bl -tag -width SIOCGIFBRDADDR 209.It Dv SIOCSIFADDR 210Set interface address for protocol family. 211Following the address assignment, the ``initialization'' routine for 212the interface is called. 213.It Dv SIOCSIFDSTADDR 214Set point to point address for protocol family and interface. 215.It Dv SIOCSIFBRDADDR 216Set broadcast address for protocol family and interface. 217.El 218.Pp 219.Xr ioctl 2 220requests to obtain addresses and requests both to set and 221retrieve other data are still fully supported 222and use the 223.Ar ifreq 224structure: 225.Bl -tag -width SIOCGIFBRDADDR 226.It Dv SIOCGIFADDR 227Get interface address for protocol family. 228.It Dv SIOCGIFDSTADDR 229Get point to point address for protocol family and interface. 230.It Dv SIOCGIFBRDADDR 231Get broadcast address for protocol family and interface. 232.It Dv SIOCSIFFLAGS 233Set interface flags field. 234If the interface is marked down, any processes currently routing 235packets through the interface are notified; some interfaces may be 236reset so that incoming packets are no longer received. 237When marked up again, the interface is reinitialized. 238.It Dv SIOCGIFFLAGS 239Get interface flags. 240.It Dv SIOCSIFMETRIC 241Set interface routing metric. 242The metric is used only by user-level routers. 243.It Dv SIOCGIFMETRIC 244Get interface metric. 245.El 246.Pp 247There are two requests that make use of a new structure: 248.Bl -tag -width SIOCGIFBRDADDR 249.It Dv SIOCAIFADDR 250An interface may have more than one address associated with it 251in some protocols. 252This request provides a means to add additional addresses (or modify 253characteristics of the primary address if the default address for 254the address family is specified). 255Rather than making separate calls to set destination or broadcast 256addresses, or network masks (now an integral feature of multiple 257protocols) a separate structure, 258.Ar ifaliasreq , 259is used to specify all three facets 260simultaneously (see below). 261One would use a slightly tailored version of this struct specific 262to each family (replacing each sockaddr by one 263of the family-specific type). 264Where the sockaddr itself is larger than the 265default size, one needs to modify the 266.Xr ioctl 2 267identifier itself to include the total size, as described in 268.Xr ioctl 2 . 269.It Dv SIOCDIFADDR 270This requests deletes the specified address from the list 271associated with an interface. 272It also uses the 273.Ar ifaliasreq 274structure to allow for the possibility of protocols allowing 275multiple masks or destination addresses, and also adopts the 276convention that specification of the default address means 277to delete the first address for the interface belonging to 278the address family in which the original socket was opened. 279.El 280.Pp 281Request making use of the 282.Ar ifconf 283structure: 284.Bl -tag -width SIOCGIFBRDADDR 285.It Dv SIOCGIFCONF 286Get interface configuration list. 287This request takes an 288.Ar ifconf 289structure (see below) as a value-result parameter. 290The 291.Ar ifc_len 292field should be initially set to the size of the buffer 293pointed to by 294.Ar ifc_buf . 295On return it will contain the length, in bytes, of the 296configuration list. 297.El 298.Bd -literal 299/* 300* Structure used in SIOC[AD]IFADDR request. 301*/ 302struct ifaliasreq { 303 char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 304 struct sockaddr ifra_addr; 305 struct sockaddr ifra_dstaddr; 306#define ifra_broadaddr ifra_dstaddr 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*/ 318struct 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 8 , 333.Xr routed 8 334.Sh HISTORY 335The 336.Nm netintro 337manual appeared in 338.Bx 4.3 Tahoe . 339