Provided by: manpages_6.03-1_all 
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. Most of them 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;
};
};
AF_INET6 is an exception. It passes an in6_ifreq structure:
struct in6_ifreq {
struct in6_addr ifr6_addr;
u32 ifr6_prefixlen;
int ifr6_ifindex; /* Interface index */
};
Normally, the user specifies which device to affect by setting ifr_name to the name of the
interface or ifr6_ifindex to the index 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.
SIOCGIFPFLAGS, SIOCSIFPFLAGS
Get or set extended (private) flags for the device. ifr_flags contains a bit mask
of the following values:
Private flags
IFF_802_1Q_VLAN Interface is 802.1Q VLAN device.
IFF_EBRIDGE Interface is Ethernet bridging device.
IFF_SLAVE_INACTIVE Interface is inactive bonding slave.
IFF_MASTER_8023AD Interface is 802.3ad bonding master.
IFF_MASTER_ALB Interface is balanced-alb bonding master.
IFF_BONDING Interface is a bonding master or slave.
IFF_SLAVE_NEEDARP Interface needs ARPs for validation.
IFF_ISATAP Interface is RFC4214 ISATAP interface.
Setting the extended (private) interface flags is a privileged operation.
SIOCGIFADDR, SIOCSIFADDR, SIOCDIFADDR
Get, set, or delete the address of the device using ifr_addr, or ifr6_addr with
ifr6_prefixlen. Setting or deleting the interface address is a privileged
operation. For compatibility, SIOCGIFADDR returns only AF_INET addresses,
SIOCSIFADDR accepts AF_INET and AF_INET6 addresses, and SIOCDIFADDR deletes only
AF_INET6 addresses. A AF_INET address can be deleted by setting it to zero via
SIOCSIFADDR.
SIOCGIFDSTADDR, SIOCSIFDSTADDR
Get or set the destination address of a point-to-point device using ifr_dstaddr.
For compatibility, only AF_INET addresses are accepted or returned. Setting the
destination address is a privileged operation.
SIOCGIFBRDADDR, SIOCSIFBRDADDR
Get or set the broadcast address for a device using ifr_brdaddr. For
compatibility, only AF_INET addresses are accepted or returned. Setting the
broadcast address is a privileged operation.
SIOCGIFNETMASK, SIOCSIFNETMASK
Get or set the network mask for a device using ifr_netmask. For compatibility,
only AF_INET addresses are accepted or returned. Setting the network mask is a
privileged operation.
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 allowed only when the interface is not up.
SIOCGIFCONF
Return a list of interface (network layer) addresses. This currently means only
addresses of the AF_INET (IPv4) family for compatibility. Unlike the others, this
ioctl passes an ifconf structure:
struct ifconf {
int ifc_len; /* size of buffer */
union {
char *ifc_buf; /* buffer address */
struct ifreq *ifc_req; /* array of structures */
};
};
If ifc_req is NULL, SIOCGIFCONF returns the necessary buffer size in bytes for
receiving all available addresses in ifc_len. Otherwise, ifc_req contains a
pointer to an array of ifreq structures to be filled with all currently active L3
interface addresses. ifc_len contains the size of the array in bytes. Within each
ifreq structure, ifr_name will receive the interface name, and ifr_addr the
address. The actual number of bytes transferred is returned in ifc_len.
If the size specified by ifc_len is insufficient to store all the addresses, the
kernel will skip the exceeding ones and return success. There is no reliable way
of detecting this condition once it has occurred. It is therefore recommended to
either determine the necessary buffer size beforehand by calling SIOCGIFCONF with
ifc_req set to NULL, or to retry the call with a bigger buffer whenever ifc_len
upon return differs by less than sizeof(struct ifreq) from its original value.
If an error occurs accessing the ifconf or ifreq structures, EFAULT will be
returned.
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
SIOCGIFCONF and the other ioctls that accept or return only AF_INET socket addresses are
IP-specific and perhaps should rather be documented 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.
AF_INET6 IPv6 addresses can be read from /proc/net/if_inet6 or via rtnetlink(7). Adding a
new IPv6 address and deleting an existing IPv6 address can be done via SIOCSIFADDR and
SIOCDIFADDR or via rtnetlink(7). Retrieving or changing destination IPv6 addresses of a
point-to-point interface is possible only 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)