man-pages/man7/netdevice.7

'\" t
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.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
.\" Permission is granted to distribute possibly modified copies
.\" of this page provided the header is included verbatim,
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.\" $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
.\"
.TH NETDEVICE  7 1999-05-02 "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.

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
.I ifreq
structure:

.nf
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 */
    };
};
.fi

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:
.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: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:T{
The addresses are lost when the interface goes down.
T}
.TE
Setting the active flag word is a privileged operation, but any
process may read it.
.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.

.nf
struct ifmap {
    unsigned long   mem_start;
    unsigned long   mem_end;
    unsigned short  base_addr;
    unsigned char   irq;
    unsigned char   dma;
    unsigned char   port;
};
.fi

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
.IR ifr_name
to
.IR ifr_newname .
This is a privileged operation.
It is only allowed 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.
The user passes a
.I ifconf
structure as argument to the ioctl.
It contains a pointer to an array of
.I ifreq
structures in
.I ifc_req
and its length in bytes in
.IR ifc_len .
The kernel fills the ifreqs with all current L3 interface addresses that
are running:
.I ifr_name
contains the interface name (eth0:1 etc.),
.I ifr_addr
the address.
The kernel returns with the actual length in
.IR ifc_len .
If
.I 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.
.\" 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
is IP specific and belongs in
.BR ip (7).
.LP
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 .
.LP
Local IPv6 IP addresses can be found via /proc/net or via
.BR rtnetlink (7).
.SH BUGS
glibc 2.1 is missing the
.I ifr_newname
macro in net/if.h.
Add the following to your program as a workaround:
.sp
.RS
.nf
#ifndef ifr_newname
#define ifr_newname     ifr_ifru.ifru_slave
#endif
.fi
.RE
.SH "SEE ALSO"
.BR proc (5),
.BR capabilities (7),
.BR ip (7),
.BR rtnetlink (7)