NETDEVICE(7)              (2020-08-13)               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.  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 set-
          ting ifr_name to the name of the interface.  All other mem-
          bers 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.


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               Retrieve the interface index of the interface into

               Get or set the active flag word of the device.
               ifr_flags contains a bit mask of the following values:
               tab(:); c s l l.  Device flags IFF_UP:Interface is run-
               ning.  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:T{ No arp
               protocol, L2 destination address not set.  T}
               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:T{ The addresses are
               lost when the interface goes down.  T}
               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:
               tab(:);     c     s     l     l.      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 mas-
               ter.  IFF_BONDING:Interface  is  a  bonding  master  or
               slave.  IFF_SLAVE_NEEDARP:Interface needs ARPs for val-
               idation.  IFF_ISATAP:Interface is RFC4214 ISATAP inter-

          Setting the extended (private) interface flags is  a  privi-
          leged operation.

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

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               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  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 implemented; 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 opera-
               tion.  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

               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 opera-

                   struct ifmap {
                       unsigned long   mem_start;
                       unsigned long   mem_end;
                       unsigned short  base_addr;
                       unsigned char   irq;

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                       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 privi-
               leged 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  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  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 return success.  There is  no  reli-
               able  way  of  detecting  this  condition  once  it has
               occurred.   It  is  therefore  recommended  to   either

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               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 struc-
               tures, 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

          In addition, some devices support private ioctls.  These are
          not described here.

          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

          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)

          This page is part of release 5.10  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

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