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NETDEVICE(7)               Linux Programmer's Manual              NETDEVICE(7)



NAME
       netdevice - Low level access to Linux network devices

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

DESCRIPTION
       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.

   Ioctls
       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.

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

       SIOCGIFINDEX
              Retrieve the interface index of the interface into ifr_ifindex.

       SIOCGIFFLAGS, SIOCSIFFLAGS
              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
                                down.
              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.

       SIOCGIFMETRIC, SIOCSIFMETRIC
              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 it.

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

       SIOCGIFHWADDR, SIOCSIFHWADDR
              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.

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

       SIOCGIFMAP, SIOCSIFMAP
              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.

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

       SIOCGIFTXQLEN, SIOCSIFTXQLEN
              Get  or  set  the transmit queue length of a device using ifr_qlen.  Setting
              the transmit queue length is a privileged operation.

       SIOCSIFNAME
              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.

       SIOCGIFCONF
              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.

NOTES
       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).

BUGS
       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
           #endif

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

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2009-01-14                      NETDEVICE(7)

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