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NETINTRO(4)                  Device Drivers Manual                 NETINTRO(4)

     netintro - introduction to networking facilities

     #include <sys/types.h>
     #include <sys/socket.h>
     #include <net/route.h>
     #include <net/if.h>

     This section is a general introduction to the networking facilities
     available in the system.  Documentation in this part of section 4 is
     broken up into three areas: protocol families (domains), protocols, and
     network interfaces.

     All network protocols are associated with a specific protocol family.  A
     protocol family provides basic services to the protocol implementation to
     allow it to function within a specific network environment.  These
     services may include packet fragmentation and reassembly, routing,
     addressing, and basic transport.  A protocol family may support multiple
     methods of addressing, though the current protocol implementations do
     not.  A protocol family normally comprises a number of protocols, one per
     socket(2) type.  It is not required that a protocol family support all
     socket types.  A protocol family may contain multiple protocols
     supporting the same socket abstraction.

     A protocol supports one of the socket abstractions detailed in socket(2).
     A specific protocol may be accessed either by creating a socket of the
     appropriate type and protocol family, or by requesting the protocol
     explicitly when creating a socket.  Protocols normally accept only one
     type of address format, usually determined by the addressing structure
     inherent in the design of the protocol family/network architecture.
     Certain semantics of the basic socket abstractions are protocol specific.
     All protocols are expected to support the basic model for their
     particular socket type, but may, in addition, provide non-standard
     facilities or extensions to a mechanism.  For example, a protocol
     supporting the SOCK_STREAM abstraction may allow more than one byte of
     out-of-band data to be transmitted per out-of-band message.

     A network interface is similar to a device interface.  Network interfaces
     comprise the lowest layer of the networking subsystem, interacting with
     the actual transport hardware.  An interface may support one or more
     protocol families and/or address formats.  The SYNOPSIS section of each
     network interface entry gives a sample specification of the related
     drivers for use in providing a system description to the config(1)

     The DIAGNOSTICS section lists messages which may appear on the console
     and/or in the system error log, /var/log/messages (see syslogd(8)), due
     to errors in device operation.

     The system currently supports the Internet protocols.  Raw socket
     interfaces are provided to the IP protocol layer of the Internet.
     Consult the appropriate manual pages in this section for more information
     regarding the support for a protocol.

     Associated with each protocol family is an address format.  All network
     address adhere to a general structure, called a sockaddr, described
     below.  However, each protocol imposes finer and more specific structure,
     generally renaming the variant, which is discussed in the protocol family
     manual page alluded to above.

           struct sockaddr {
                   u_char  sa_len;
                   u_char  sa_family;
                   char    sa_data[14];

     The field sa_len contains the total length of the of the structure, which
     may exceed 16 bytes.  The following address values for sa_family are
     known to the system (and additional formats are defined for possible
     future implementation):

     #define    AF_LOCAL     1    /* local to host */
     #define    AF_INET      2    /* internetwork: UDP, TCP, etc. */
     #define    AF_NS        6    /* Xerox NS protocols */
     #define    AF_CCITT     10   /* CCITT protocols, X.25 etc */
     #define    AF_HYLINK    15   /* NSC Hyperchannel */
     #define    AF_INET6     24   /* internetwork, v6: UDP, TCP, etc. */

     UNIX provides some packet routing facilities.  The kernel maintains a
     routing information database, which is used in selecting the appropriate
     network interface when transmitting packets.

     A user process (or possibly multiple co-operating processes) maintains
     this database by sending messages over a special kind of socket.  This
     supplants fixed size ioctl(2) used in earlier releases.

     This facility is described in route(4).

     Each network interface in a system corresponds to a path through which
     messages may be sent and received.  A network interface usually has a
     hardware device associated with it, though certain interfaces such as the
     loopback interface, lo(4), do not.

     The following ioctl(2) calls may be used to manipulate network
     interfaces.  The ioctl(2) is made on a socket (typically of type
     SOCK_DGRAM) in the desired domain.  Most of the requests supported in
     earlier releases take an ifreq structure as its parameter.  This
     structure has the form

     struct  ifreq {
     #define    IFNAMSIZ    16
         char    ifr_name[IFNAMSIZ];         /* if name, e.g. "en0" */
         union {
             struct    sockaddr ifru_addr;
             struct    sockaddr ifru_dstaddr;
             struct    sockaddr ifru_broadaddr;
             short     ifru_flags;
             int       ifru_metric;
             void   *ifru_data;
         } ifr_ifru;
     #define ifr_addr      ifr_ifru.ifru_addr    /* address */
     #define ifr_dstaddr   ifr_ifru.ifru_dstaddr /* other end of p-to-p link */
     #define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
     #define ifr_space     ifr_ifru.ifru_space     /* sockaddr_storage */
     #define ifr_flags     ifr_ifru.ifru_flags   /* flags */
     #define ifr_metric    ifr_ifru.ifru_metric  /* metric */
     #define ifr_mtu       ifr_ifru.ifru_mtu       /* mtu */
     #define ifr_dlt       ifr_ifru.ifru_dlt       /* data link type (DLT_*) */
     #define ifr_value     ifr_ifru.ifru_value     /* generic value */
     #define ifr_media     ifr_ifru.ifru_metric    /* media options (overload) */
     #define ifr_data      ifr_ifru.ifru_data    /* for use by interface */
     #define ifr_buf       ifr_ifru.ifru_b.b_buf   /* new interface ioctls */
     #define ifr_buflen    ifr_ifru.ifru_b.b_buflen
     #define ifr_index     ifr_ifru.ifru_value     /* interface index */

     Calls which are now deprecated are:

     SIOCSIFADDR     Set interface address for protocol family.  Following the
                     address assignment, the ``initialization'' routine for
                     the interface is called.

     SIOCSIFDSTADDR  Set point to point address for protocol family and

     SIOCSIFBRDADDR  Set broadcast address for protocol family and interface.

     ioctl(2) requests to obtain addresses and requests both to set and
     retrieve other data are still fully supported and use the ifreq

     SIOCGIFADDR     Get interface address for protocol family.

     SIOCGIFDSTADDR  Get point to point address for protocol family and

     SIOCGIFBRDADDR  Get broadcast address for protocol family and interface.

     SIOCSIFFLAGS    Set interface flags field.  If the interface is marked
                     down, any processes currently routing packets through the
                     interface are notified; some interfaces may be reset so
                     that incoming packets are no longer received.  When
                     marked up again, the interface is reinitialized.

     SIOCGIFFLAGS    Get interface flags.

     SIOCSIFMETRIC   Set interface routing metric.  The metric is used only by
                     user-level routers.

     SIOCGIFMETRIC   Get interface metric.

     SIOCGIFINDEX    Get the interface index and populate ifr_index.

     There are two requests that make use of a new structure:

     SIOCAIFADDR     An interface may have more than one address associated
                     with it in some protocols.  This request provides a means
                     to add additional addresses (or modify characteristics of
                     the primary address if the default address for the
                     address family is specified).  Rather than making
                     separate calls to set destination or broadcast addresses,
                     or network masks (now an integral feature of multiple
                     protocols) a separate structure, ifaliasreq, is used to
                     specify all three facets simultaneously (see below).  One
                     would use a slightly tailored version of this struct
                     specific to each family (replacing each sockaddr by one
                     of the family-specific type).  Where the sockaddr itself
                     is larger than the default size, one needs to modify the
                     ioctl(2) identifier itself to include the total size, as
                     described in ioctl(2).

     SIOCDIFADDR     This requests deletes the specified address from the list
                     associated with an interface.  It also uses the
                     ifaliasreq structure to allow for the possibility of
                     protocols allowing multiple masks or destination
                     addresses, and also adopts the convention that
                     specification of the default address means to delete the
                     first address for the interface belonging to the address
                     family in which the original socket was opened.

     SIOCGIFALIAS    This request provides means to get additional addresses
                     together with netmask and broadcast/destination from an
                     interface.  It also uses the ifaliasreq structure.

     Request making use of the ifconf structure:

     SIOCGIFCONF     Get interface configuration list.  This request takes an
                     ifconf structure (see below) as a value-result parameter.
                     The ifc_len field should be initially set to the size of
                     the buffer pointed to by ifc_buf.  On return it will
                     contain the length, in bytes, of the configuration list.

     * Structure used in SIOC[AD]IFADDR request.
     struct ifaliasreq {
             char    ifra_name[IFNAMSIZ];   /* if name, e.g. "en0" */
             struct  sockaddr        ifra_addr;
             struct  sockaddr        ifra_dstaddr;
     #define ifra_broadaddr  ifra_dstaddr
             struct  sockaddr        ifra_mask;

     * Structure used in SIOCGIFCONF request.
     * Used to retrieve interface configuration
     * for machine (useful for programs which
     * must know all networks accessible).
     struct ifconf {
         int   ifc_len;              /* size of associated buffer */
         union {
             void    *ifcu_buf;
             struct     ifreq *ifcu_req;
         } ifc_ifcu;
     #define ifc_buf ifc_ifcu.ifcu_buf /* buffer address */
     #define ifc_req ifc_ifcu.ifcu_req /* array of structures returned */

     config(1), ioctl(2), socket(2), intro(4), routed(8)

     The netintro manual appeared in 4.3BSD-Tahoe.

NetBSD 10.99                    August 2, 2018                    NetBSD 10.99