NETDEVICE

netdevice ? Low level access to Linux network devices.

#include <sys/ioctl.h> #include <net/if.h>

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.

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 bitmask of the following values:

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. 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_ifindex to ifr_newname. This is a privileged operation.

SIOCGIFCONF

Return a list of interface (transport layer) addresses. This currently means only addresses of the AF_INET 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 it is equal the original length the user should assume that it overflowed and retry with a bigger buffer. When no error occurs the ioctl returns 0; otherwise -1. Overflow is no 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.

Strictly seen 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.

ip(7), proc(7)