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 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.  Most of them 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;

       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  effec-
       tive  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  con-
              tains 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 it.

              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 opera-

              Get or set the address of the device  using  ifr_addr.   Setting
              the  interface  address is a privileged operation.  For compati-
              bility, 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 compatibility, only AF_INET addresses are  accepted  or  re-
              turned.   Setting  the  broadcast address is a privileged opera-

              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  implemented;  it sets ifr_metric to 0 if you at-
              tempt 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;

              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  allowed
              only when the interface is not up.

              Return a list of interface (network layer) addresses.  This cur-
              rently means only addresses of the  AF_INET  (IPv4)  family  for
              compatibility.   Unlike  the others, this ioctl passes an ifconf

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

              If ifc_req is NULL, SIOCGIFCONF  returns  the  necessary  buffer
              size  in bytes for receiving all available addresses in ifc_len.
              Otherwise, ifc_req contains a  pointer  to  an  array  of  ifreq
              structures  to  be filled with all currently active L3 interface
              addresses.  ifc_len contains the size of  the  array  in  bytes.
              Within each ifreq structure, ifr_name will receive the interface
              name, and ifr_addr the address.   The  actual  number  of  bytes
              transferred is returned in ifc_len.

              If  the  size  specified by ifc_len is insufficient to store all
              the addresses, the kernel will skip the exceeding ones  and  re-
              turn success.  There is no reliable way of detecting this condi-
              tion once it has occurred.  It is therefore recommended  to  ei-
              ther  determine  the necessary buffer size beforehand by calling
              SIOCGIFCONF with ifc_req set to NULL, or to retry the call  with
              a  bigger  buffer  whenever  ifc_len upon return differs by less
              than sizeof(struct ifreq) from its original value.

              If an error occurs accessing the  ifconf  or  ifreq  structures,
              EFAULT will be returned.

       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 de-
       scribed here.

       Strictly speaking, SIOCGIFCONF and the other ioctls that accept or  re-
       turn  only  AF_INET  socket  addresses,  are  IP-specific and belong in

       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 5.05 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at

Linux                             2019-11-19                      NETDEVICE(7)
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