netdevice(7) — Linux manual page


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

NAME         top

       netdevice - low-level access to Linux network devices

SYNOPSIS         top

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

DESCRIPTION         top

       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.  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

              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_br‐
              daddr.  For compatibility, only AF_INET addresses are accepted
              or returned.  Setting the broadcast address  is  a  privileged

              Get  or  set  the network mask for a device using ifr_netmask.
              For compatibility, only AF_INET addresses are accepted or  re‐
              turned.  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_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  de‐
              vice 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  privi‐
              leged 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

              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
              currently means only addresses of the  AF_INET  (IPv4)  family
              for  compatibility.   Unlike  the others, this ioctl passes an
              ifconf structure:

                  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 in‐
              terface 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 con‐
              dition once it has occurred.  It is therefore  recommended  to
              either determine the necessary buffer size beforehand by call‐
              ing 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-spe‐
       cific interface options.  See the protocol man pages for  a  descrip‐
       tion.  For configuring IP addresses, see ip(7).

       In  addition, some devices support private ioctls.  These are not de‐
       scribed here.

NOTES         top

       SIOCGIFCONF and the other ioctls that accept or return only AF_INET
       socket addresses are IP-specific and perhaps should rather be
       documented 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

BUGS         top

       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

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.09 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                            2020-08-13                     NETDEVICE(7)

Pages that refer to this page: freeifaddrs(3)getifaddrs(3)ip(7)ipv6(7)packet(7)rtnetlink(7)