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       netdevice - Low level access to Linux network devices


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


       This  man  page  describes  the  sockets  interface  which  is  used to
       configure 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

              Retrieve the interface index of the interface into ifr_ifindex.

              Get or set the  active  flag  word  of  the  device.   ifr_flags
              contains a bit mask of the following values:

                                         Device flags
              IFF_UP            Interface is running.
              IFF_BROADCAST     Valid broadcast address set.
              IFF_DEBUG         Internal debugging flag.
              IFF_LOOPBACK      Interface is a loopback interface.
              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_family 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;

              The interpretation of the ifmap structure depends on the  device
              driver and the architecture.

              Add  an  address  to or delete an address from the device's link
              layer multicast filters using ifr_hwaddr.  These are  privileged
              operations.  See also packet(7) for an alternative.

              Get or set the transmit queue length of a device using ifr_qlen.
              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
              structures 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  buffer  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
       following to your program as a workaround:

           #ifndef ifr_newname
           #define ifr_newname     ifr_ifru.ifru_slave


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


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