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



NAME
       netdevice - Low level access to Linux network devices

SYNOPSIS
       #include <&lt;sys/ioctl.h>&gt;
       #include <&lt;net/if.h>&gt;

DESCRIPTION
       This  man page describes the sockets interface which is used to config-
       ure 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  con-
              tains a bit mask of the following values:

              tab(:);  c  s  l  l.   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_RUN-
              NING:Resources  allocated.  IFF_NOARP:No arp protocol, L2 desti-
              nation address not set.  IFF_PROMISC:Interface is in promiscuous
              mode.    IFF_NOTRAILERS:Avoid   use   of   trailers.    IFF_ALL-
              MULTI:Receive all multicast  packets.   IFF_MASTER:Master  of  a
              load balancing bundle.  IFF_SLAVE:Slave of a load balancing bun-
              dle.  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  inter-
              face goes down.  T} 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_fam-
              ily  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 struc-
              tures 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 buf-
              fer 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 &lt;net/if.h&gt;.  Add the fol-
       lowing 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 3.05 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             1999-05-02                      NETDEVICE(7)