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 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 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 3.24 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/.