#include <sys/ioctl.h>
       #include <net/if.h>

       This  man page describes the sockets interface which is used to config-
       ure network devices.

       Linux supports some standard ioctls to configure network devices.  They
       can be used on any socket's file descriptor regardless of the family or
       type.  They pass an ifreq structure:

           struct ifreq {
               char ifr_name[IFNAMSIZ]; /* Interface name */
               union {
                   struct sockaddr ifr_addr;
                   struct sockaddr ifr_dstaddr;
                   struct sockaddr ifr_broadaddr;
                   struct sockaddr ifr_netmask;
                   struct sockaddr ifr_hwaddr;
                   short           ifr_flags;
                   int             ifr_ifindex;
                   int             ifr_metric;
                   int             ifr_mtu;
                   struct ifmap    ifr_map;
                   char            ifr_slave[IFNAMSIZ];
                   char            ifr_newname[IFNAMSIZ];
                   char           *ifr_data;

           struct ifconf {
               int                 ifc_len; /* size of buffer */
               union {
                   char           *ifc_buf; /* buffer address */
                   struct ifreq   *ifc_req; /* array of structures */

       Normally, the user specifies which device to affect by setting ifr_name
       to  the  name of the interface.  All other members of the structure may
       share memory.

       If an ioctl is marked as privileged then using it requires an effective
       user  ID of 0 or the CAP_NET_ADMIN capability.  If this is not the case
       EPERM will be returned.

              Given the ifr_ifindex, return  the  name  of  the  interface  in
              ifr_name.   This  is  the only ioctl which returns its result in

              IFF_POINTOPOINT   Interface is a point-to-point link.
              IFF_RUNNING       Resources allocated.
              IFF_NOARP         No arp protocol, L2 destination address not set.
              IFF_PROMISC       Interface is in promiscuous mode.
              IFF_NOTRAILERS    Avoid use of trailers.
              IFF_ALLMULTI      Receive all multicast packets.
              IFF_MASTER        Master of a load balancing bundle.
              IFF_SLAVE         Slave of a load balancing bundle.
              IFF_MULTICAST     Supports multicast
              IFF_PORTSEL       Is able to select media type via ifmap.
              IFF_AUTOMEDIA     Auto media selection active.
              IFF_DYNAMIC       The  addresses  are lost when the interface goes
              IFF_LOWER_UP      Driver signals L1 up (since Linux 2.6.17)
              IFF_DORMANT       Driver signals dormant (since Linux 2.6.17)
              IFF_ECHO          Echo sent packets (since Linux 2.6.25)

              Setting the active flag word is a privileged operation, but  any
              process may read it.

              Get  or  set the metric of the device using ifr_metric.  This is
              currently not implemented;  it  sets  ifr_metric  to  0  if  you
              attempt  to read it and returns EOPNOTSUPP if you attempt to set

              Get or set the MTU (Maximum Transfer Unit)  of  a  device  using
              ifr_mtu.   Setting  the  MTU is a privileged operation.  Setting
              the MTU to too small values may cause kernel crashes.

              Get or set the hardware address of a  device  using  ifr_hwaddr.
              The hardware address is specified in a struct sockaddr.  sa_fam-
              ily contains the ARPHRD_* device type, sa_data the  L2  hardware
              address starting from byte 0.  Setting the hardware address is a
              privileged operation.

              Set the hardware broadcast address of a device from  ifr_hwaddr.
              This is a privileged operation.

              Get  or  set  the interface's hardware parameters using ifr_map.
              Setting the parameters is a privileged operation.

                  struct ifmap {
                      unsigned long   mem_start;
                      unsigned long   mem_end;
                      unsigned short  base_addr;
                      unsigned char   irq;
                      unsigned char   dma;
                      unsigned char   port;

              Setting the transmit queue length is a privileged operation.

              Changes the name of  the  interface  specified  in  ifr_name  to
              ifr_newname.   This  is  a  privileged  operation.   It  is only
              allowed when the interface is not up.

              Return a list of interface (transport  layer)  addresses.   This
              currently  means only addresses of the AF_INET (IPv4) family for
              compatibility.  The user passes a ifconf structure  as  argument
              to the ioctl.  It contains a pointer to an array of ifreq struc-
              tures in ifc_req and its length in bytes in ifc_len.  The kernel
              fills  the  ifreqs  with all current L3 interface addresses that
              are running: ifr_name contains the interface name (eth0:1 etc.),
              ifr_addr the address.  The kernel returns with the actual length
              in ifc_len.  If ifc_len is equal to the original length the buf-
              fer  probably  has overflowed and you should retry with a bigger
              buffer to get all addresses.  When no  error  occurs  the  ioctl
              returns 0; otherwise -1.  Overflow is not an error.

       Most  protocols support their own ioctls to configure protocol-specific
       interface options.  See the protocol man pages for a description.   For
       configuring IP addresses see ip(7).

       In  addition  some  devices  support  private  ioctls.   These  are not
       described here.

       Strictly speaking, SIOCGIFCONF is IP specific and belongs in ip(7).

       The names of interfaces with  no  addresses  or  that  don't  have  the
       IFF_RUNNING flag set can be found via /proc/net/dev.

       Local IPv6 IP addresses can be found via /proc/net or via rtnetlink(7).

       glibc 2.1 is missing the ifr_newname macro in <net/if.h>.  Add the fol-
       lowing to your program as a workaround:

           #ifndef ifr_newname
           #define ifr_newname     ifr_ifru.ifru_slave

       proc(5), capabilities(7), ip(7), rtnetlink(7)

       This page is part of release 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at
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