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



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 capa-
       bility.  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 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2009-01-14                      NETDEVICE(7)