'\" t

.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.

.\"

.\" %%%LICENSE_START(VERBATIM_ONE_PARA)

.\" Permission is granted to distribute possibly modified copies

.\" of this page provided the header is included verbatim,

.\" and in case of nontrivial modification author and date

.\" of the modification is added to the header.

.\" %%%LICENSE_END

.\"

.\" $Id: netdevice.7,v 1.10 2000/08/17 10:09:54 ak Exp $

.\"

.\" Modified, 2004-11-25, mtk, formatting and a few wording fixes

.\"

.\" Modified, 2011-11-02, <bidulock@openss7.org>, added many basic

.\"  but missing ioctls, such as SIOCGIFADDR.

.\"

.TH NETDEVICE  7 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

netdevice \- low-level access to Linux network devices

.SH SYNOPSIS

.B "#include <sys/ioctl.h>"

.br

.B "#include <net/if.h>"

.SH DESCRIPTION

This man page describes the sockets interface which is used to configure

network devices.

.PP

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

.I ifreq

structure:

.PP

.in +4n

.EX

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;

    };

};

.EE

.in

.PP

Normally, the user specifies which device to affect by setting

.I ifr_name

to the name of the interface.

All other members of the structure may

share memory.

.SS Ioctls

If an ioctl is marked as privileged, then using it requires an effective

user ID of 0 or the

.B CAP_NET_ADMIN

capability.

If this is not the case,

.B EPERM

will be returned.

.TP

.B SIOCGIFNAME

Given the

.IR ifr_ifindex ,

return the name of the interface in

.IR ifr_name .

This is the only ioctl which returns its result in

.IR ifr_name .

.TP

.B SIOCGIFINDEX

Retrieve the interface index of the interface into

.IR ifr_ifindex .

.TP

.BR SIOCGIFFLAGS ", " SIOCSIFFLAGS

Get or set the active flag word of the device.

.I ifr_flags

contains a bit mask of the following values:

.\" Do not right adjust text blocks in tables

.na

.TS

tab(:);

c s

l l.

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:T{

No arp protocol, L2 destination address not set.

T}

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:T{

The addresses are lost when the interface goes down.

T}

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)

.TE

.ad

.PP

Setting the active flag word is a privileged operation, but any

process may read it.

.TP

.BR SIOCGIFPFLAGS ", " SIOCSIFPFLAGS

Get or set extended (private) flags for the device.

.I ifr_flags

contains a bit mask of the following values:

.TS

tab(:);

c s

l l.

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.

.TE

.PP

Setting the extended (private) interface flags is a privileged operation.

.TP

.BR SIOCGIFADDR ", " SIOCSIFADDR

Get or set the address of the device using

.IR ifr_addr .

Setting the interface address is a privileged operation.

For compatibility, only

.B AF_INET

addresses are accepted or returned.

.TP

.BR SIOCGIFDSTADDR ", " SIOCSIFDSTADDR

Get or set the destination address of a point-to-point device using

.IR ifr_dstaddr .

For compatibility, only

.B AF_INET

addresses are accepted or returned.

Setting the destination address is a privileged operation.

.TP

.BR SIOCGIFBRDADDR ", " SIOCSIFBRDADDR

Get or set the broadcast address for a device using

.IR ifr_brdaddr .

For compatibility, only

.B AF_INET

addresses are accepted or returned.

Setting the broadcast address is a privileged operation.

.TP

.BR SIOCGIFNETMASK ", " SIOCSIFNETMASK

Get or set the network mask for a device using

.IR ifr_netmask .

For compatibility, only

.B AF_INET

addresses are accepted or returned.

Setting the network mask is a privileged operation.

.TP

.BR SIOCGIFMETRIC ", " SIOCSIFMETRIC

Get or set the metric of the device using

.IR ifr_metric .

This is currently not implemented; it sets

.I ifr_metric

to 0 if you attempt to read it and returns

.B EOPNOTSUPP

if you attempt to set it.

.TP

.BR SIOCGIFMTU ", " SIOCSIFMTU

Get or set the MTU (Maximum Transfer Unit) of a device using

.IR ifr_mtu .

Setting the MTU is a privileged operation.

Setting the MTU to

too small values may cause kernel crashes.

.TP

.BR SIOCGIFHWADDR ", " SIOCSIFHWADDR

Get or set the hardware address of a device using

.IR ifr_hwaddr .

The hardware address is specified in a struct

.IR sockaddr .

.I sa_family

contains the ARPHRD_* device type,

.I sa_data

the L2 hardware address starting from byte 0.

Setting the hardware address is a privileged operation.

.TP

.B SIOCSIFHWBROADCAST

Set the hardware broadcast address of a device from

.IR ifr_hwaddr .

This is a privileged operation.

.TP

.BR SIOCGIFMAP ", " SIOCSIFMAP

Get or set the interface's hardware parameters using

.IR ifr_map .

Setting the parameters is a privileged operation.

.IP

.in +4n

.EX

struct ifmap {

    unsigned long   mem_start;

    unsigned long   mem_end;

    unsigned short  base_addr;

    unsigned char   irq;

    unsigned char   dma;

    unsigned char   port;

};

.EE

.in

.IP

The interpretation of the ifmap structure depends on the device driver

and the architecture.

.TP

.BR SIOCADDMULTI ", " SIOCDELMULTI

Add an address to or delete an address from the device's link layer

multicast filters using

.IR ifr_hwaddr .

These are privileged operations.

See also

.BR packet (7)

for an alternative.

.TP

.BR SIOCGIFTXQLEN ", " SIOCSIFTXQLEN

Get or set the transmit queue length of a device using

.IR ifr_qlen .

Setting the transmit queue length is a privileged operation.

.TP

.B SIOCSIFNAME

Changes the name of the interface specified in

.I ifr_name

to

.IR ifr_newname .

This is a privileged operation.

It is allowed only when the interface

is not up.

.TP

.B SIOCGIFCONF

Return a list of interface (transport layer) addresses.

This currently

means only addresses of the

.B AF_INET

(IPv4) family for compatibility.

Unlike the others, this ioctl passes an

.I ifconf

structure:

.IP

.in +4n

.EX

struct ifconf {

    int                 ifc_len; /* size of buffer */

    union {

        char           *ifc_buf; /* buffer address */

        struct ifreq   *ifc_req; /* array of structures */

    };

};

.EE

.in

.IP

If

.I ifc_req

is NULL,

.B SIOCGIFCONF

returns the necessary buffer size in bytes

for receiving all available addresses in

.IR ifc_len .

Otherwise,

.I ifc_req

contains a pointer to an array of

.I ifreq

structures to be filled with all currently active L3 interface addresses.

.I ifc_len

contains the size of the array in bytes.

Within each

.I ifreq

structure,

.I ifr_name

will receive the interface name, and

.I ifr_addr

the address.

The actual number of bytes transferred is returned in

.IR ifc_len .

.IP

If the size specified by

.I 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

.B SIOCGIFCONF

with

.I ifc_req

set to NULL, or to retry the call with a bigger buffer whenever

.I ifc_len

upon return differs by less than

.I sizeof(struct ifreq)

from its original value.

.IP

If an error occurs accessing the

.I ifconf

or

.I ifreq

structures,

.B EFAULT

will be returned.

.\" Slaving isn't supported in 2.2

.\" .

.\" .TP

.\" .BR SIOCGIFSLAVE ", " SIOCSIFSLAVE

.\" Get or set the slave device using

.\" .IR ifr_slave .

.\" Setting the slave device is a privileged operation.

.\" .PP

.\" FIXME . add amateur radio stuff.

.PP

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

.BR ip (7).

.PP

In addition, some devices support private ioctls.

These are not described here.

.SH NOTES

Strictly speaking,

.B SIOCGIFCONF

and the other ioctls that accept or return only

.B AF_INET

socket addresses,

are IP-specific and belong in

.BR ip (7).

.PP

The names of interfaces with no addresses or that don't have the

.B IFF_RUNNING

flag set can be found via

.IR /proc/net/dev .

.PP

Local IPv6 IP addresses can be found via

.I /proc/net

or via

.BR rtnetlink (7).

.SH BUGS

glibc 2.1 is missing the

.I ifr_newname

macro in

.IR <net/if.h> .

Add the following to your program as a workaround:

.PP

.in +4n

.EX

#ifndef ifr_newname

#define ifr_newname     ifr_ifru.ifru_slave

#endif

.EE

.in

.SH SEE ALSO

.BR proc (5),

.BR capabilities (7),

.BR ip (7),

.BR rtnetlink (7)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.