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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.  Setting  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  multicast
              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 3.35 of the Linux man-pages project.  A  description  of  the
       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.