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


         This section is a general introduction to the networking facilities
         available in the system.  Documentation in this part of section 4 is bro-
         ken 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 ser-
         vices may include packet fragmentation and reassembly, routing, address-
         ing, and basic transport.  A protocol family may support multiple methods
         of addressing, though the current protocol implementations do not.  A
         protocol family is normally comprised of 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 support-
         ing 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.  Cer-
         tain semantics of the basic socket abstractions are protocol specific.
         All protocols are expected to support the basic model for their particu-
         lar 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 pro-
         tocol families and/or address formats.  The SYNOPSIS section of each net-
         work interface entry gives a sample specification of the related drivers
         for use in providing a system description to the config(8) program.  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, the Xerox Network
         Systems(tm) protocols, and some of the ISO OSI protocols.  Raw socket
         interfaces are provided to the IP protocol layer of the Internet, and to
         the IDP protocol of Xerox NS.  Consult the appropriate manual pages in
         this section for more information regarding the support for each protocol
         The field sa_len contains the total length 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 imple-
         #define    AF_UNIX      1    /* local to host (pipes, portals) */
         #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_ISO       18   /* ISO protocols */


         FreeBSD 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 inter-
         faces.  The ioctl() 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;
                 struct    ifreq_buffer ifru_buffer;
                 short     ifru_flags[2];
                 short     ifru_index;
                 int       ifru_metric;
                 int       ifru_mtu;
                 int       ifru_phys;
                 int       ifru_media;
                 caddr_t   ifru_data;
                 int       ifru_cap[2];
             } ifr_ifru;
         #define ifr_addr      ifr_ifru.ifru_addr      /* address */
         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 inter-
         SIOCSIFBRDADDR  Set broadcast address for protocol family and interface.
         Ioctl() requests to obtain addresses and requests both to set and
         retrieve other data are still fully supported and use the ifreq struc-
         SIOCGIFADDR     Get interface address for protocol family.
         SIOCGIFDSTADDR  Get point to point address for protocol family and inter-
         SIOCGIFBRDADDR  Get broadcast address for protocol family and interface.
         SIOCSIFCAP      Attempt to set the enabled capabilities field for the
                         interface to the value of the ifr_reqcap field of the
                         ifreq structure.  Note that, depending on the particular
                         interface features, some capabilities may appear hard-
                         coded to enabled, or toggling a capability may affect the
                         status of other ones.  The supported capabilities field
                         is read-only, and the ifr_curcap field is unused by this
         SIOCGIFCAP      Get the interface capabilities fields.  The values for
                         supported and enabled capabilities will be returned in
                         the ifr_reqcap and ifr_curcap fields of the ifreq struc-
                         ture, respectively.
         SIOCGIFDESCR    Get the interface description, returned in the buffer
                         field of ifru_buffer struct.  The user supplied buffer
                         length should be defined in the length field of
                         ifru_buffer struct passed in as parameter, and the length
                         would include the terminating nul character.  If there is
                         not enough space to hold the interface length, no copy
                         would be done and the buffer field of ifru_buffer would
                         be set to NULL.  The kernel will store the buffer length
                         in the length field upon return, regardless whether the
                         buffer itself is sufficient to hold the data.
         SIOCSIFDESCR    Set the interface description to the value of the buffer
                         field of ifru_buffer struct, with length field specifying
                         its length (counting the terminating nul).
                         face name is given without a unit number the system will
                         attempt to create a new interface with an arbitrary unit
                         number.  On successful return the ifr_name field will
                         contain the new interface name.
         SIOCIFDESTROY   Attempt to destroy the specified interface.
         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 sepa-
                         rate calls to set destination or broadcast addresses, or
                         network masks (now an integral feature of multiple proto-
                         cols) a separate structure 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-spe-
                         cific type).  Where the sockaddr itself is larger than
                         the default size, one needs to modify the ioctl() identi-
                         fier itself to include the total size, as described in
         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 pro-
                         tocols 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.
         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 con-
                         tain the length, in bytes, of the configuration list.
         SIOCIFGCLONERS  Get list of clonable interfaces.  This request takes an
                         if_clonereq structure (see below) as a value-result
                         parameter.  The ifcr_count field should be set to the
                         number of IFNAMSIZ sized strings that can be fit in the
                         buffer pointed to by ifcr_buffer.  On return, ifcr_total
                         will be set to the number of clonable interfaces and the
                         buffer pointed to by ifcr_buffer will be filled with the
                         names of clonable interfaces aligned on IFNAMSIZ bound-
         * Structure used in SIOCAIFCONF request.
         struct ifconf {
             int   ifc_len;              /* size of associated buffer */
             union {
                 caddr_t    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 */
         /* Structure used in SIOCIFGCLONERS request. */
         struct if_clonereq {
                 int     ifcr_total;     /* total cloners (out) */
                 int     ifcr_count;     /* room for this many in user buffer */
                 char    *ifcr_buffer;   /* buffer for cloner names */
         /* Structure used in SIOCGIFDESCR and SIOCSIFDESCR requests */
         struct ifreq_buffer {
                 size_t  length;         /* length of the buffer */
                 void   *buffer;         /* pointer to userland space buffer */


         ioctl(2), socket(2), intro(4), config(8), routed(8), ifnet(9)


         The netintro manual appeared in 4.3BSD-Tahoe.

    BSD April 14, 2010 BSD


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