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

       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 ifr_name.

              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
              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

              Get  or set extended (private) flags for the device.  ifr_flags contains a bit mask
              of the following values:

                                      Private flags
              IFF_802_1Q_VLAN      Interface is 802.1Q VLAN device.
              IFF_EBRIDGE          Interface is Ethernet bridging device.
              IFF_SLAVE_INACTIVE   Interface is inactive bonding slave.
              IFF_MASTER_8023AD    Interface is 802.3ad bonding master.
              IFF_MASTER_ALB       Interface is balanced-alb bonding master.
              IFF_BONDING          Interface is a bonding master or slave.
              IFF_SLAVE_NEEDARP    Interface needs ARPs for validation.
              IFF_ISATAP           Interface is RFC4214 ISATAP interface.

              Setting the extended (private) interface flags is a privileged operation.

              Get or set the address of the device using ifr_addr.  Setting the interface address
              is  a privileged operation.  For compatibility, only AF_INET addresses are accepted
              or returned.

              Get or set the destination address of a point-to-point  device  using  ifr_dstaddr.
              For  compatibility,  only  AF_INET addresses are accepted or returned.  Setting the
              destination address is a privileged operation.

              Get or set the broadcast address for a device using ifr_brdaddr.   For  compatibil-
              ity,  only  AF_INET  addresses  are  accepted  or  returned.  Setting the broadcast
              address is a privileged operation.

              Get or set the network mask for a device  using  ifr_netmask.   For  compatibility,
              only  AF_INET  addresses  are  accepted or returned.  Setting the network mask is a
              privileged operation.

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

              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 ker-
              nel 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 privi-
              leged operation.

              Get or set the interface's hardware parameters using ifr_map.  Setting the  parame-
              ters 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

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

              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 allowed only 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  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 and the other ioctls that accept  or  return  only  AF_INET
       socket addresses, are IP specific and belong 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  pro-
       gram 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 3.53 of the Linux man-pages project.  A description of the
       project,    and    information    about    reporting    bugs,    can    be    found     at

Linux                                       2012-04-26                               NETDEVICE(7)

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