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.
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:
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_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 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.
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: