if(7)                  DEVICES AND MODULES                  if(7)



NAME
     if - general properties of Internet Protocol network  inter-
     faces

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  SIOCSIF-
     NAME  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  inter-
     faces  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 Ether-
     nets 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, e.g. "emd1" */
             union {
                     struct  sockaddr ifruaddr;
                     struct  sockaddr ifrudstaddr;
                     char    ifruoname[IFNAMSIZ];     /* other if name */
                     struct  sockaddr ifrubroadaddr;



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                     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 */
     #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  inter-
                         face.

     SIOCGIFDSTADDR      Get point to point  address  for  inter-
                         face.

     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.













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     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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