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 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 sockaddrifr_addr;
struct sockaddrifr_dstaddr;
struct sockaddrifr_broadaddr;
struct sockaddrifr_netmask;
struct sockaddrifr_hwaddr;
short ifr_flags;
int ifr_ifindex;
int ifr_metric;
int ifr_mtu;
struct ifmapifr_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.
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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 val-
ues:
tab(:); c s l l. Device flags IFF_UP:Interface is
running. IFF_BROADCAST:Valid broadcast address
set. IFF_DEBUG:Internal debugging flag. IFF_LOOP-
BACK: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_ALL-
MULTI:Receive all multicast packets. IFF_MAS-
TER: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_AUTOME-
DIA:Auto media selection active. IFF_DYNAMIC:T{
The addresses are lost when the interface goes
down. T}
Setting the active flag word is a privileged opera-
tion, but any process may read it.
SIOCGIFMETRIC, SIOCSIFMETRIC
Get or set the metric of the device using ifr_met-
ric. 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 privi-
leged operation. Setting the MTU to too small val-
ues 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
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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 privi-
leged 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 cur-
rent 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
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the original length the buffer probably has over-
flowed and you should retry with a bigger buffer to
get all addresses. When no error occurs the ioctl
returns 0; otherwise -1. Overflow is no error.
Most protocols support their own ioctls to configure pro-
tocol 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 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.
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 workaround:
#ifndef ifr_newname
#define ifr_newname ifr_ifru.ifru_slave
#endif
SEE ALSO
ip(7), proc(7), rtnetlink(7)
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