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NETDEVICE(7)		   Linux Programmers Manual		 NETDEVICE(7)



NAME
       netdevice - Low level access to Linux network devices

SYNOPSIS
       #include 
       #include 

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 sockets 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 interfaces 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	devices  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
	      buffer probably has overflowed and you should retry with a  big
	      ger 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 dont 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 .  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)




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