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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 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:

					 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.
	      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 <net/if.h>.  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 3.15 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)
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