if(7)                        UNIX System V(TCP/IP)                        if(7)


NAME
      if - general properties of Internet Protocol network interfaces

DESCRIPTION
      A network interface is a device for sending and receiving packets on a
      network.  A network interface is usually a hardware device, although
      certain interfaces such as the loopback interface, lo(7), are implemented
      in software.  Network interfaces used by the Internet Protocol (IP) must
      be STREAMS devices conforming to the Datalink Provider Interface (DLPI).

      An interface becomes available to IP when it is linked below the IP
      STREAMS device with the ILINK ioctl() call.  This may be initiated by
      the kernel at boot time or by a user program some time after the system
      is running.  Each IP interface must have a name assigned to it with the
      SIOCSIFNAME ioctl().  This name is used as a unique handle on the
      interface by all of the other network interface ioctl() calls.  Each
      interface must be assigned an IP address with the SIOCSIFADDR ioctl()
      before it can be used.  On interfaces where the network-to-link layer
      address mapping is static, only the network number is taken from the
      ioctl() request; the remainder is found in a hardware specific manner.
      On interfaces which provide dynamic network-to-link layer address mapping
      facilities [for example, 10Mb/s Ethernets using arp(7)], the entire
      address specified in the ioctl() is used.  A routing table entry for
      destinations on the network of the interface is installed automatically
      when an interface's address is set.

IOCTLS
      The following ioctl() calls may be used to manipulate IP network
      interfaces.  Unless specified otherwise, the request takes an ifreq
      structure as its parameter.  This structure has the form:

      /* Interface request structure used for socket ioctl's.  All */
      /* interface ioctl's must have parameter definitions which */
      /* begin with ifrname.  The remainder may be interface specific. */
      struct  ifreq {
      #define IFNAMSIZ     16
          char         ifrname[IFNAMSIZ];      /* if name, for example "emd1" */
          union {
               struct  sockaddr ifruaddr;
               struct  sockaddr ifrudstaddr;
               char    ifruoname[IFNAMSIZ];        /* other if name */
               struct  sockaddr ifrubroadaddr;
               short   ifruflags;
               int     ifrumetric;
               char    ifrudata[1];                /* interface dependent data */
               char    ifruenaddr[6];
          } ifrifru;
      #define ifraddr      ifrifru.ifruaddr      /* address */
      #define ifrdstaddr   ifrifru.ifrudstaddr   /* other end of p-to-p link */
      #define ifroname     ifrifru.ifruoname     /* other if name */
      #define ifrbroadaddr ifrifru.ifrubroadaddr /* broadcast address */
      #define ifrflags     ifrifru.ifruflags     /* flags */


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if(7)                        UNIX System V(TCP/IP)                        if(7)


      #define ifrmetric    ifrifru.ifrumetric    /* metric */
      #define ifrdata      ifrifru.ifrudata      /* for use by interface */
      #define ifrenaddr    ifrifru.ifruenaddr    /* ethernet address */
      };

      SIOCSIFADDR         Set interface address.  Following the address
                          assignment, the initialization routine for the
                          interface is called.

      SIOCGIFADDR         Get interface address.

      SIOCSIFDSTADDR      Set point to point address for interface.

      SIOCGIFDSTADDR      Get point to point address for interface.

      SIOCSIFFLAGS        Set interface flags field.  If the interface is
                          marked down, any processes currently routing packets
                          through the interface are notified.

      SIOCGIFFLAGS        Get interface flags.

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

      The ifconf structure has the form:

            /*
             * Structure used in SIOCGIFCONF request.
             * Used to retrieve interface configuration
             * for machine (useful for programs which
             * must know all networks accessible).
             */
            struct      ifconf {
                  int     ifclen;           /* size of associated buffer */
                  union {
                          caddrt ifcubuf;
                          struct  ifreq *ifcureq;
                  } ifcifcu;
            #define ifcbuf ifcifcu.ifcubuf  /* buffer address */
            #define ifcreq ifcifcu.ifcureq  /* array of structures returned */
            };

      SIOCSIFNAME
            Set the name of the interface.

SEE ALSO
      arp(7), ip(7), lo(7)



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