1.\" $OpenBSD: netintro.4,v 1.53 2018/07/09 09:18:52 schwarze 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: July 9 2018 $ 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#define IFNAMSIZ 16 205 char ifr_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 206 union { 207 struct sockaddr ifru_addr; 208 struct sockaddr ifru_dstaddr; 209 struct sockaddr ifru_broadaddr; 210 short ifru_flags; 211 int ifru_metric; 212 int64_t ifru_vnetid; 213 uint64_t ifru_media; 214 caddr_t ifru_data; 215 unsigned int ifru_index; 216 } ifr_ifru; 217#define ifr_addr ifr_ifru.ifru_addr /* address */ 218#define ifr_dstaddr ifr_ifru.ifru_dstaddr /* other end of p-to-p link */ 219#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */ 220#define ifr_flags ifr_ifru.ifru_flags /* flags */ 221#define ifr_metric ifr_ifru.ifru_metric /* metric */ 222#define ifr_mtu ifr_ifru.ifru_metric /* mtu (overload) */ 223#define ifr_hardmtu ifr_ifru.ifru_metric /* hardmtu (overload) */ 224#define ifr_media ifr_ifru.ifru_media /* media options */ 225#define ifr_rdomainid ifr_ifru.ifru_metric /* VRF instance (overload) */ 226#define ifr_vnetid ifr_ifru.ifru_vnetid /* Virtual Net Id */ 227#define ifr_ttl ifr_ifru.ifru_metric /* tunnel TTL (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}; 232.Ed 233.Pp 234The supported 235.Xr ioctl 2 236requests are: 237.Bl -tag -width Ds 238.It Dv SIOCSIFADDR Fa "struct ifreq *" 239Set the interface address for a protocol family. 240Following the address assignment, the 241.Dq initialization 242routine for the 243interface is called. 244.Pp 245This call has been deprecated and superseded by the 246.Dv SIOCAIFADDR 247call, described below. 248.It Dv SIOCSIFDSTADDR Fa "struct ifreq *" 249Set the point-to-point address for a protocol family and interface. 250.Pp 251This call has been deprecated and superseded by the 252.Dv SIOCAIFADDR 253call, described below. 254.It Dv SIOCSIFBRDADDR Fa "struct ifreq *" 255Set the broadcast address for a protocol family and interface. 256.Pp 257This call has been deprecated and superseded by the 258.Dv SIOCAIFADDR 259call, described below. 260.It Dv SIOCGIFADDR Fa "struct ifreq *" 261Get the interface address for a protocol family. 262.It Dv SIOCGIFDSTADDR Fa "struct ifreq *" 263Get the point-to-point address for a protocol family and interface. 264.It Dv SIOCGIFBRDADDR Fa "struct ifreq *" 265Get the broadcast address for a protocol family and interface. 266.It Dv SIOCGIFDESCR Fa "struct ifreq *" 267Get the interface description, returned in the 268.Va ifru_data 269field. 270.It Dv SIOCSIFDESCR Fa "struct ifreq *" 271Set the interface description to the value of the 272.Va ifru_data 273field, limited to the size of 274.Dv IFDESCRSIZE . 275.It Dv SIOCSIFFLAGS Fa "struct ifreq *" 276Set the interface flags. 277If the interface is marked down, any processes currently routing packets 278through the interface are notified; some interfaces may be reset so that 279incoming packets are no longer received. 280When marked up again, the interface is reinitialized. 281.It Dv SIOCGIFFLAGS Fa "struct ifreq *" 282Get the interface flags. 283.It Dv SIOCGIFXFLAGS Fa "struct ifreq *" 284Get the extended interface flags. 285.It Dv SIOCGIFMTU Fa "struct ifreq *" 286Get the current MTU of the interface. 287.It Dv SIOCGIFHARDMTU Fa "struct ifreq *" 288Get the maximum hardware MTU of the interface. 289.It Dv SIOCSIFMEDIA Fa "struct ifreq *" 290Set the interface media settings. 291See 292.Xr ifmedia 4 293for possible values. 294.It Dv SIOCGIFMEDIA Fa "struct ifmediareq *" 295Get the interface media settings. 296The 297.Vt ifmediareq 298structure is as follows: 299.Bd -literal 300struct ifmediareq { 301 char ifm_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 302 uint64_t ifm_current; /* current media options */ 303 uint64_t ifm_mask; /* don't care mask */ 304 uint64_t ifm_status; /* media status */ 305 uint64_t ifm_active; /* active options */ 306 int ifm_count; /* #entries in ifm_ulist array */ 307 uint64_t *ifm_ulist; /* media words */ 308}; 309.Ed 310.Pp 311See 312.Xr ifmedia 4 313for interpreting this value. 314.It Dv SIOCSIFMETRIC Fa "struct ifreq *" 315Set the interface routing metric. 316The metric is used only by user-level routers. 317.It Dv SIOCGIFMETRIC Fa "struct ifreq *" 318Get the interface metric. 319.It Dv SIOCSIFPRIORITY Fa "struct ifreq *" 320Set the interface routing priority. 321The interface routing priority influences the resulting routing priority of 322new static routes added to the kernel using the specified interface. 323The value is in the range of 0 to 16 with smaller numbers being better. 324.It Dv SIOCGIFPRIORITY Fa "struct ifreq *" 325Get the interface priority. 326.It Dv SIOCGIFRDOMAIN Fa "struct ifreq *" 327Get the interface routing domain. 328This identifies which routing table is used for the interface. 329.It Dv SIOCAIFADDR Fa "struct ifaliasreq *" 330An interface may have more than one address associated with it 331in some protocols. 332This request provides a means to add additional addresses (or modify 333characteristics of the primary address if the default address for the 334address family is specified). 335.Pp 336Rather than making separate calls to set destination or broadcast addresses, 337or network masks (now an integral feature of multiple protocols), a separate 338structure, 339.Vt ifaliasreq , 340is used to specify all three facets simultaneously (see below). 341One would use a slightly tailored version of this structure specific 342to each family (replacing each 343.Vt sockaddr 344by one 345of the family-specific type). 346One should always set the length of a 347.Vt sockaddr , 348as described in 349.Xr ioctl 2 . 350.Pp 351The 352.Vt ifaliasreq 353structure is as follows: 354.Bd -literal 355struct ifaliasreq { 356 char ifra_name[IFNAMSIZ]; /* if name, e.g. "en0" */ 357 struct sockaddr ifra_addr; 358 struct sockaddr ifra_dstaddr; 359#define ifra_broadaddr ifra_dstaddr 360 struct sockaddr ifra_mask; 361}; 362.Ed 363.It Dv SIOCDIFADDR Fa "struct ifreq *" 364This request deletes the specified address from the list 365associated with an interface. 366It also uses the 367.Vt ifaliasreq 368structure to allow for the possibility of protocols allowing 369multiple masks or destination addresses, and also adopts the 370convention that specification of the default address means 371to delete the first address for the interface belonging to 372the address family in which the original socket was opened. 373.It Dv SIOCGIFCONF Fa "struct ifconf *" 374Get the interface configuration list. 375This request takes an 376.Vt ifconf 377structure (see below) as a value-result parameter. 378The 379.Va ifc_len 380field should be initially set to the size of the buffer 381pointed to by 382.Va ifc_buf . 383On return it will contain the length, in bytes, of the 384configuration list. 385.Pp 386Alternately, if the 387.Va ifc_len 388passed in is set to 0, 389.Dv SIOCGIFCONF 390will set 391.Va ifc_len 392to the size that 393.Va ifc_buf 394needs to be to fit the entire configuration list and will not 395fill in the other parameters. 396This is useful for determining the exact size that 397.Va ifc_buf 398needs to be in advance. 399Note, however, that this is an extension 400that not all operating systems support. 401.Bd -literal 402struct ifconf { 403 int ifc_len; /* size of associated buffer */ 404 union { 405 caddr_t ifcu_buf; 406 struct ifreq *ifcu_req; 407 } ifc_ifcu; 408#define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */ 409#define ifc_req ifc_ifcu.ifcu_req /* array of structures ret'd */ 410}; 411.Ed 412.It Dv SIOCIFCREATE Fa "struct ifreq *" 413Attempt to create the specified interface. 414.It Dv SIOCIFDESTROY Fa "struct ifreq *" 415Attempt to destroy the specified interface. 416.It Dv SIOCIFGCLONERS Fa "struct if_clonereq *" 417Get the list of clonable interfaces. 418This request takes an 419.Vt if_clonereq 420structure pointer (see below) as a value-result parameter. 421The 422.Va ifcr_count 423field should be set to the number of 424.Dv IFNAMSIZ Ns -sized 425strings that can fit in the buffer pointed to by 426.Va ifcr_buffer . 427On return, 428.Va ifcr_total 429will be set to the number of clonable interfaces, and the buffer pointed 430to by 431.Va ifcr_buffer 432will be filled with the names of clonable interfaces aligned on 433.Dv IFNAMSIZ 434boundaries. 435.Pp 436The 437.Vt if_clonereq 438structure is as follows: 439.Bd -literal 440struct if_clonereq { 441 int ifcr_total; /* total cloners (out) */ 442 int ifcr_count; /* room for this many in user buf */ 443 char *ifcr_buffer; /* buffer for cloner names */ 444}; 445.Ed 446.It Dv SIOCAIFGROUP Fa "struct ifgroupreq *" 447Associate the interface named by 448.Va ifgr_name 449with the interface group named by 450.Va ifgr_group . 451The 452.Vt ifgroupreq 453structure is as follows: 454.Bd -literal 455struct ifg_req { 456 char ifgrq_group[IFNAMSIZ]; 457}; 458 459struct ifgroupreq { 460 char ifgr_name[IFNAMSIZ]; 461 u_int ifgr_len; 462 union { 463 char ifgru_group[IFNAMSIZ]; 464 struct ifg_req *ifgru_groups; 465 } ifgr_ifgru; 466#define ifgr_group ifgr_ifgru.ifgru_group 467#define ifgr_groups ifgr_ifgru.ifgru_groups 468}; 469.Ed 470.It Dv SIOCGIFGROUP Fa "struct ifgroupreq *" 471Retrieve the list of groups for which an interface is a member. 472The interface is named by 473.Va ifgr_name . 474On enter, the amount of memory in which the group names will 475be written is stored in 476.Va ifgr_len , 477and the group names themselves will be written to the memory 478pointed to by 479.Va ifgr_groups . 480On return, the amount of memory actually written is returned in 481.Va ifgr_len . 482.Pp 483Alternately, if the 484.Va ifgr_len 485passed in is set to 0, 486.Dv SIOCGIFGROUP 487will set 488.Va ifgr_len 489to the size that 490.Va ifgr_groups 491needs to be to fit the entire group list and will not 492fill in the other parameters. 493This is useful for determining the exact size that 494.Va ifgr_groups 495needs to be in advance. 496.It Dv SIOCDIFGROUP Fa "struct ifgroupreq *" 497Remove the membership of the interface named by 498.Va ifgr_name 499from the group 500.Va ifgr_group . 501.El 502.Sh SEE ALSO 503.Xr netstat 1 , 504.Xr ioctl 2 , 505.Xr socket 2 , 506.Xr arp 4 , 507.Xr bridge 4 , 508.Xr ifmedia 4 , 509.Xr inet 4 , 510.Xr intro 4 , 511.Xr ip 4 , 512.Xr ip6 4 , 513.Xr lo 4 , 514.Xr mpe 4 , 515.Xr pf 4 , 516.Xr tcp 4 , 517.Xr udp 4 , 518.Xr unix 4 , 519.Xr hosts 5 , 520.Xr bgpd 8 , 521.Xr config 8 , 522.Xr ifconfig 8 , 523.Xr mrouted 8 , 524.Xr netstart 8 , 525.Xr ospfd 8 , 526.Xr ripd 8 , 527.Xr route 8 528.Sh HISTORY 529The 530.Nm 531manual appeared in 532.Bx 4.3 Tahoe . 533