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       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

           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;

       AF_INET6 is an exception.  It passes an in6_ifreq structure:

           struct in6_ifreq {
               struct in6_addr     ifr6_addr;
               u32                 ifr6_prefixlen;
               int                 ifr6_ifindex; /* Interface index */

       Normally, the user specifies which device to affect by setting ifr_name to the name of the
       interface or ifr6_ifindex to the index  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 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 operation.

              Get,  set,  or  delete  the address of the device using ifr_addr, or ifr6_addr with
              ifr6_prefixlen.   Setting  or  deleting  the  interface  address  is  a  privileged
              operation.    For   compatibility,  SIOCGIFADDR  returns  only  AF_INET  addresses,
              SIOCSIFADDR accepts AF_INET and AF_INET6 addresses, and  SIOCDIFADDR  deletes  only
              AF_INET6  addresses.   A  AF_INET  address can be deleted by setting it to zero via

              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  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 device driver and the

              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  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  reliable  way
              of  detecting  this condition once it has occurred.  It is therefore recommended to
              either 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

       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.


       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.

       AF_INET6 IPv6 addresses can be read from /proc/net/if_inet6 or via rtnetlink(7).  Adding a
       new  IPv6  address  and  deleting an existing IPv6 address can be done via SIOCSIFADDR and
       SIOCDIFADDR or via rtnetlink(7).  Retrieving or changing destination IPv6 addresses  of  a
       point-to-point interface is possible only via rtnetlink(7).


       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)


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