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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.  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;
               };
           };

       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.

   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.

       SIOCGIFPFLAGS
       SIOCSIFPFLAGS
              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.

       SIOCGIFADDR
       SIOCSIFADDR
       SIOCDIFADDR
              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 SIOCSIFADDR.

       SIOCGIFDSTADDR
       SIOCSIFDSTADDR
              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.

       SIOCGIFBRDADDR
       SIOCSIFBRDADDR
              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.

       SIOCGIFNETMASK
       SIOCSIFNETMASK
              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.

       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 allowed only when the interface is not up.

       SIOCGIFCONF
              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 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 described here.

NOTES

       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).

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)