1.\" $OpenBSD: netintro.4,v 1.55 2024/09/23 20:38:49 kn Exp $ 2.\" $NetBSD: netintro.4,v 1.4 1995/10/19 08:03:40 jtc Exp $ 3.\" 4.\" Copyright (c) 1983, 1990, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)netintro.4 8.2 (Berkeley) 11/30/93 32.\" 33.Dd $Mdocdate: September 23 2024 $ 34.Dt NETINTRO 4 35.Os 36.Sh NAME 37.Nm netintro 38.Nd introduction to networking facilities 39.Sh SYNOPSIS 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 57implementation to allow it to function within a specific 58network environment. 59These services may include packet fragmentation and reassembly, routing, 60addressing, and basic transport. 61A protocol family may support multiple methods of addressing, though 62the current protocol implementations do not. 63A protocol family is normally comprised of a number of protocols, one per 64.Xr socket 2 65type. 66It is not required that a protocol family support all socket types. 67A protocol family may contain multiple protocols supporting the same socket 68abstraction. 69.Pp 70A protocol supports one of the socket abstractions detailed in 71.Xr socket 2 . 72A specific protocol may be accessed either by creating a 73socket of the appropriate type and protocol family, or 74by requesting the protocol explicitly when creating a socket. 75Protocols normally accept only one type of address format, 76usually determined by the addressing structure inherent in 77the design of the protocol family/network architecture. 78Certain semantics of the basic socket abstractions are 79protocol specific. 80All protocols are expected to support the basic model for their particular 81socket type, but may, in addition, provide non-standard facilities or 82extensions to a mechanism. 83For example, a protocol supporting the 84.Dv SOCK_STREAM 85abstraction may allow more than one byte of out-of-band 86data to be transmitted per out-of-band message. 87.Pp 88A network interface is similar to a device interface. 89Network interfaces comprise the lowest layer of the 90networking subsystem, interacting with the actual transport 91hardware. 92An interface may support one or more protocol families and/or address formats. 93The SYNOPSIS section of each network interface entry gives a sample 94specification of the related drivers for use in providing a system description 95to the 96.Xr config 8 97program. 98The DIAGNOSTICS section lists messages which may appear on the console 99and/or in the system error log, 100.Pa /var/log/messages 101(see 102.Xr syslogd 8 ) , 103due to errors in device operation. 104.Pp 105Network interfaces may be collected together into interface groups. 106An interface group is a container that can be used generically when 107referring to any interface related by some criteria. 108When an action is performed on an interface group, such as packet 109filtering by the 110.Xr pf 4 111subsystem, the operation will be applied to each member interface in the 112group, if supported by the subsystem. 113The 114.Xr ifconfig 8 115utility can be used to view and assign membership of an interface to an 116interface group with the 117.Cm group 118modifier. 119.Sh PROTOCOLS 120The system currently supports the 121Internet protocols (IPv4 and IPv6), 122MPLS, 123and a few others. 124Raw socket interfaces are provided to the IP protocol 125layer of the 126Internet. 127Consult the appropriate manual pages in this section for more 128information regarding the support for each protocol family. 129.Sh ADDRESSING 130Associated with each protocol family is an address 131format. 132All network addresses adhere to a general structure, called a 133.Vt sockaddr , 134described below. 135However, each protocol imposes a finer, more specific structure, generally 136renaming the variant, which is discussed in the protocol family manual 137page alluded to above. 138.Bd -literal -offset indent 139struct sockaddr { 140 u_int8_t sa_len; /* total length */ 141 sa_family_t sa_family; /* address family */ 142 char sa_data[14]; /* actually longer */ 143}; 144.Ed 145.Pp 146The field 147.Va sa_len 148contains the total length of the structure, 149which may exceed 16 bytes. 150The following address values for 151.Va sa_family 152are known to the system 153(and additional formats are defined for possible future implementation): 154.Bd -literal 155#define AF_UNIX 1 /* local to host */ 156#define AF_INET 2 /* internetwork: UDP, TCP, etc. */ 157#define AF_INET6 24 /* IPv6 */ 158#define AF_MPLS 33 /* Multiprotocol Label Switching */ 159.Ed 160.Pp 161The 162.Va sa_data 163field contains the actual address value. 164Note that it may be longer than 14 bytes. 165.Sh ROUTING 166.Ox 167provides some packet routing facilities. 168The kernel maintains a routing information database, which 169is used in selecting the appropriate network interface when 170transmitting packets. 171.Pp 172A user process (or possibly multiple co-operating processes) 173maintains this database by sending messages over a special kind 174of socket. 175This supplants fixed-size 176.Xr ioctl 2 Ns s 177used in earlier releases. 178.Pp 179This facility is described in 180.Xr route 4 . 181.Sh INTERFACES 182Each network interface in a system corresponds to a 183path through which messages may be sent and received. 184A network interface usually has a hardware device associated with it, 185though certain interfaces such as the loopback interface, 186.Xr lo 4 , 187do not. 188.Pp 189The following 190.Xr ioctl 2 191calls may be used to manipulate network interfaces. 192The 193.Xr ioctl 2 194is made on a socket (typically of type 195.Dv SOCK_DGRAM ) 196in the desired domain. 197Most of the requests 198take an 199.Vt ifreq 200structure pointer as their parameter. 201This structure is as follows: 202.Bd -literal 203struct ifreq { 204 char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 205 union { 206 struct sockaddr ifru_addr; 207 struct sockaddr ifru_dstaddr; 208 struct sockaddr ifru_broadaddr; 209 short ifru_flags; 210 int ifru_metric; 211 int64_t ifru_vnetid; 212 uint64_t ifru_media; 213 caddr_t ifru_data; 214 unsigned int ifru_index; 215 } ifr_ifru; 216#define ifr_addr ifr_ifru.ifru_addr /* address */ 217#define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */ 218#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */ 219#define ifr_flags ifr_ifru.ifru_flags /* flags */ 220#define ifr_metric ifr_ifru.ifru_metric /* metric */ 221#define ifr_mtu ifr_ifru.ifru_metric /* mtu (overload) */ 222#define ifr_hardmtu ifr_ifru.ifru_metric /* hardmtu (overload) */ 223#define ifr_media ifr_ifru.ifru_media /* media options */ 224#define ifr_rdomainid ifr_ifru.ifru_metric /* VRF instance (overload) */ 225#define ifr_vnetid ifr_ifru.ifru_vnetid /* Virtual Net Id */ 226#define ifr_ttl ifr_ifru.ifru_metric /* tunnel TTL (overload) */ 227#define ifr_df ifr_ifru.ifru_metric /* tunnel DF (overload) */ 228#define ifr_data ifr_ifru.ifru_data /* for use by interface */ 229#define ifr_index ifr_ifru.ifru_index /* interface index */ 230#define ifr_llprio ifr_ifru.ifru_metric /* link layer priority */ 231#define ifr_hdrprio ifr_ifru.ifru_metric /* header prio field config */ 232#define ifr_pwe3 ifr_ifru.ifru_metric /* PWE3 type */ 233}; 234.Ed 235.Pp 236The supported 237.Xr ioctl 2 238requests are: 239.Bl -tag -width Ds 240.It Dv SIOCSIFADDR Fa "struct ifreq *" 241Set the interface address for a protocol family. 242Following the address assignment, the 243.Dq initialization 244routine for the 245interface is called. 246.Pp 247This call has been deprecated and superseded by the 248.Dv SIOCAIFADDR 249call, described below. 250.It Dv SIOCSIFDSTADDR Fa "struct ifreq *" 251Set the point-to-point address for a protocol family and interface. 252.Pp 253This call has been deprecated and superseded by the 254.Dv SIOCAIFADDR 255call, described below. 256.It Dv SIOCSIFBRDADDR Fa "struct ifreq *" 257Set the broadcast address for a protocol family and interface. 258.Pp 259This call has been deprecated and superseded by the 260.Dv SIOCAIFADDR 261call, described below. 262.It Dv SIOCGIFADDR Fa "struct ifreq *" 263Get the interface address for a protocol family. 264.It Dv SIOCGIFDSTADDR Fa "struct ifreq *" 265Get the point-to-point address for a protocol family and interface. 266.It Dv SIOCGIFBRDADDR Fa "struct ifreq *" 267Get the broadcast address for a protocol family and interface. 268.It Dv SIOCGIFDESCR Fa "struct ifreq *" 269Get the interface description, returned in the 270.Va ifru_data 271field. 272.It Dv SIOCSIFDESCR Fa "struct ifreq *" 273Set the interface description to the value of the 274.Va ifru_data 275field, limited to the size of 276.Dv IFDESCRSIZE . 277.It Dv SIOCSIFFLAGS Fa "struct ifreq *" 278Set the interface flags. 279If the interface is marked down, any processes currently routing packets 280through the interface are notified; some interfaces may be reset so that 281incoming packets are no longer received. 282When marked up again, the interface is reinitialized. 283.It Dv SIOCGIFFLAGS Fa "struct ifreq *" 284Get the interface flags. 285.It Dv SIOCGIFXFLAGS Fa "struct ifreq *" 286Get the extended interface flags. 287.It Dv SIOCSIFMTU Fa "struct ifreq *" 288Set the MTU of the interface. 289.It Dv SIOCGIFMTU Fa "struct ifreq *" 290Get the current MTU of the interface. 291.It Dv SIOCGIFHARDMTU Fa "struct ifreq *" 292Get the maximum hardware MTU of the interface. 293.It Dv SIOCSIFMEDIA Fa "struct ifreq *" 294Set the interface media settings. 295See 296.Xr ifmedia 4 297for possible values. 298.It Dv SIOCGIFMEDIA Fa "struct ifmediareq *" 299Get the interface media settings. 300The 301.Vt ifmediareq 302structure is as follows: 303.Bd -literal 304struct ifmediareq { 305 char ifm_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 306 uint64_t ifm_current; /* get/set current media options */ 307 uint64_t ifm_mask; /* don't care mask */ 308 uint64_t ifm_status; /* media status */ 309 uint64_t ifm_active; /* active options */ 310 int ifm_count; /* # entries in ifm_ulist array */ 311 uint64_t *ifm_ulist; /* media words */ 312}; 313.Ed 314.Pp 315See 316.Xr ifmedia 4 317for interpreting this value. 318.It Dv SIOCSIFMETRIC Fa "struct ifreq *" 319Set the interface routing metric. 320The metric is used only by user-level routers. 321.It Dv SIOCGIFMETRIC Fa "struct ifreq *" 322Get the interface metric. 323.It Dv SIOCSIFPRIORITY Fa "struct ifreq *" 324Set the interface routing priority. 325The interface routing priority influences the resulting routing priority of 326new static routes added to the kernel using the specified interface. 327The value is in the range of 0 to 16 with smaller numbers being better. 328.It Dv SIOCGIFPRIORITY Fa "struct ifreq *" 329Get the interface priority. 330.It Dv SIOCGIFRDOMAIN Fa "struct ifreq *" 331Get the interface routing domain. 332This identifies which routing table is used for the interface. 333.It Dv SIOCAIFADDR Fa "struct ifaliasreq *" 334An interface may have more than one address associated with it 335in some protocols. 336This request provides a means to add additional addresses (or modify 337characteristics of the primary address if the default address for the 338address family is specified). 339.Pp 340Rather than making separate calls to set destination or broadcast addresses, 341or network masks (now an integral feature of multiple protocols), a separate 342structure, 343.Vt ifaliasreq , 344is used to specify all three facets simultaneously (see below). 345One would use a slightly tailored version of this structure specific 346to each family (replacing each 347.Vt sockaddr 348by one 349of the family-specific type). 350One should always set the length of a 351.Vt sockaddr , 352as described in 353.Xr ioctl 2 . 354.Pp 355The 356.Vt ifaliasreq 357structure is as follows: 358.Bd -literal 359struct ifaliasreq { 360 char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 361 union { 362 struct sockaddr ifrau_addr; 363 int ifrau_align; 364 } ifra_ifrau; 365#ifndef ifra_addr 366#define ifra_addr ifra_ifrau.ifrau_addr 367#endif 368 struct sockaddr ifra_dstaddr; 369#define ifra_broadaddr ifra_dstaddr 370 struct sockaddr ifra_mask; 371}; 372.Ed 373.It Dv SIOCDIFADDR Fa "struct ifreq *" 374This request deletes the specified address from the list 375associated with an interface. 376It also uses the 377.Vt ifaliasreq 378structure to allow for the possibility of protocols allowing 379multiple masks or destination addresses, and also adopts the 380convention that specification of the default address means 381to delete the first address for the interface belonging to 382the address family in which the original socket was opened. 383.It Dv SIOCGIFCONF Fa "struct ifconf *" 384Get the interface configuration list. 385This request takes an 386.Vt ifconf 387structure (see below) as a value-result parameter. 388The 389.Va ifc_len 390field should be initially set to the size of the buffer 391pointed to by 392.Va ifc_buf . 393On return it will contain the length, in bytes, of the 394configuration list. 395.Pp 396Alternately, if the 397.Va ifc_len 398passed in is set to 0, 399.Dv SIOCGIFCONF 400will set 401.Va ifc_len 402to the size that 403.Va ifc_buf 404needs to be to fit the entire configuration list and will not 405fill in the other parameters. 406This is useful for determining the exact size that 407.Va ifc_buf 408needs to be in advance. 409Note, however, that this is an extension 410that not all operating systems support. 411.Bd -literal 412struct ifconf { 413 int ifc_len; /* size of associated buffer */ 414 union { 415 caddr_t ifcu_buf; 416 struct ifreq *ifcu_req; 417 } ifc_ifcu; 418#define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */ 419#define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */ 420}; 421.Ed 422.It Dv SIOCIFCREATE Fa "struct ifreq *" 423Attempt to create the specified interface. 424.It Dv SIOCIFDESTROY Fa "struct ifreq *" 425Attempt to destroy the specified interface. 426.It Dv SIOCIFGCLONERS Fa "struct if_clonereq *" 427Get the list of clonable interfaces. 428This request takes an 429.Vt if_clonereq 430structure pointer (see below) as a value-result parameter. 431The 432.Va ifcr_count 433field should be set to the number of 434.Dv IFNAMSIZ Ns -sized 435strings that can fit in the buffer pointed to by 436.Va ifcr_buffer . 437On return, 438.Va ifcr_total 439will be set to the number of clonable interfaces, and the buffer pointed 440to by 441.Va ifcr_buffer 442will be filled with the names of clonable interfaces aligned on 443.Dv IFNAMSIZ 444boundaries. 445.Pp 446The 447.Vt if_clonereq 448structure is as follows: 449.Bd -literal 450struct if_clonereq { 451 int ifcr_total; /* total cloners (out) */ 452 int ifcr_count; /* room for this many in user buffer */ 453 char *ifcr_buffer; /* buffer for cloner names */ 454}; 455.Ed 456.It Dv SIOCAIFGROUP Fa "struct ifgroupreq *" 457Associate the interface named by 458.Va ifgr_name 459with the interface group named by 460.Va ifgr_group . 461The 462.Vt ifgroupreq 463structure is as follows: 464.Bd -literal 465struct ifg_req { 466 union { 467 char ifgrqu_group[IFNAMSIZ]; 468 char ifgrqu_member[IFNAMSIZ]; 469 } ifgrq_ifgrqu; 470#define ifgrq_group ifgrq_ifgrqu.ifgrqu_group 471#define ifgrq_member ifgrq_ifgrqu.ifgrqu_member 472}; 473 474struct ifgroupreq { 475 char ifgr_name[IFNAMSIZ]; 476 u_int ifgr_len; 477 union { 478 char ifgru_group[IFNAMSIZ]; 479 struct ifg_req *ifgru_groups; 480 struct ifg_attrib ifgru_attrib; 481 } ifgr_ifgru; 482#define ifgr_group ifgr_ifgru.ifgru_group 483#define ifgr_groups ifgr_ifgru.ifgru_groups 484#define ifgr_attrib ifgr_ifgru.ifgru_attrib 485}; 486.Ed 487.It Dv SIOCGIFGROUP Fa "struct ifgroupreq *" 488Retrieve the list of groups for which an interface is a member. 489The interface is named by 490.Va ifgr_name . 491On enter, the amount of memory in which the group names will 492be written is stored in 493.Va ifgr_len , 494and the group names themselves will be written to the memory 495pointed to by 496.Va ifgr_groups . 497On return, the amount of memory actually written is returned in 498.Va ifgr_len . 499.Pp 500Alternately, if the 501.Va ifgr_len 502passed in is set to 0, 503.Dv SIOCGIFGROUP 504will set 505.Va ifgr_len 506to the size that 507.Va ifgr_groups 508needs to be to fit the entire group list and will not 509fill in the other parameters. 510This is useful for determining the exact size that 511.Va ifgr_groups 512needs to be in advance. 513.It Dv SIOCDIFGROUP Fa "struct ifgroupreq *" 514Remove the membership of the interface named by 515.Va ifgr_name 516from the group 517.Va ifgr_group . 518.El 519.Sh SEE ALSO 520.Xr netstat 1 , 521.Xr ioctl 2 , 522.Xr socket 2 , 523.Xr arp 4 , 524.Xr bridge 4 , 525.Xr ifmedia 4 , 526.Xr inet 4 , 527.Xr intro 4 , 528.Xr ip 4 , 529.Xr ip6 4 , 530.Xr lo 4 , 531.Xr mpe 4 , 532.Xr pf 4 , 533.Xr tcp 4 , 534.Xr udp 4 , 535.Xr unix 4 , 536.Xr hosts 5 , 537.Xr bgpd 8 , 538.Xr config 8 , 539.Xr ifconfig 8 , 540.Xr mrouted 8 , 541.Xr netstart 8 , 542.Xr ospfd 8 , 543.Xr ripd 8 , 544.Xr route 8 545.Sh HISTORY 546The 547.Nm 548manual appeared in 549.Bx 4.3 Tahoe . 550