ifconfig
IFCONFIG(8) Linux Programmer’s Manual IFCONFIG(8)
NAME
ifconfig - configure a network interface
SYNOPSIS
ifconfig [interface]
ifconfig interface [aftype] options | address ...
DESCRIPTION
Ifconfig is used to configure the kernel-resident network interfaces.
It is used at boot time to set up interfaces as necessary. After
that, it is usually only needed when debugging or when system tuning
is needed.
If no arguments are given, ifconfig displays the status of the cur-
rently active interfaces. If a single interface argument is given, it
displays the status of the given interface only; if a single -a argu-
ment is given, it displays the status of all interfaces, even those
that are down. Otherwise, it configures an interface.
Address Families
If the first argument after the interface name is recognized as the
name of a supported address family, that address family is used for
decoding and displaying all protocol addresses. Currently supported
address families include inet (TCP/IP, default), inet6 (IPv6), ax25
(AMPR Packet Radio), ddp (Appletalk Phase 2), ipx (Novell IPX) and
netrom (AMPR Packet radio).
OPTIONS
interface
The name of the interface. This is usually a driver name fol-
lowed by a unit number, for example eth0 for the first Ethernet
interface.
up This flag causes the interface to be activated. It is implic-
itly specified if an address is assigned to the interface.
down This flag causes the driver for this interface to be shut down.
[-]arp Enable or disable the use of the ARP protocol on this inter-
face.
[-]promisc
Enable or disable the promiscuous mode of the interface. If
selected, all packets on the network will be received by the
interface.
[-]allmulti
Enable or disable all-multicast mode. If selected, all multi-
cast packets on the network will be received by the interface.
metric N
This parameter sets the interface metric.
mtu N This parameter sets the Maximum Transfer Unit (MTU) of an
interface.
dstaddr addr
Set the remote IP address for a point-to-point link (such as
PPP). This keyword is now obsolete; use the pointopoint key-
word instead.
netmask addr
Set the IP network mask for this interface. This value
defaults to the usual class A, B or C network mask (as derived
from the interface IP address), but it can be set to any value.
add addr/prefixlen
Add an IPv6 address to an interface.
del addr/prefixlen
Remove an IPv6 address from an interface.
tunnel aa.bb.cc.dd
Create a new SIT (IPv6-in-IPv4) device, tunnelling to the given
destination.
irq addr
Set the interrupt line used by this device. Not all devices
can dynamically change their IRQ setting.
io_addr addr
Set the start address in I/O space for this device.
mem_start addr
Set the start address for shared memory used by this device.
Only a few devices need this.
media type
Set the physical port or medium type to be used by the device.
Not all devices can change this setting, and those that can
vary in what values they support. Typical values for type are
10base2 (thin Ethernet), 10baseT (twisted-pair 10Mbps Ether-
net), AUI (external transceiver) and so on. The special medium
type of auto can be used to tell the driver to auto-sense the
media. Again, not all drivers can do this.
[-]broadcast [addr]
If the address argument is given, set the protocol broadcast
address for this interface. Otherwise, set (or clear) the
IFF_BROADCAST flag for the interface.
[-]pointopoint [addr]
This keyword enables the point-to-point mode of an interface,
meaning that it is a direct link between two machines with
nobody else listening on it.
If the address argument is also given, set the protocol address
of the other side of the link, just like the obsolete dstaddr
keyword does. Otherwise, set or clear the IFF_POINTOPOINT flag
for the interface.
hw class address
Set the hardware address of this interface, if the device
driver supports this operation. The keyword must be followed
by the name of the hardware class and the printable ASCII
equivalent of the hardware address. Hardware classes currently
supported include ether (Ethernet), ax25 (AMPR AX.25), ARCnet
and netrom (AMPR NET/ROM).
multicast
Set the multicast flag on the interface. This should not nor-
mally be needed as the drivers set the flag correctly them-
selves.
address
The IP address to be assigned to this interface.
txqueuelen length
Set the length of the transmit queue of the device. It is use-
ful to set this to small values for slower devices with a high
latency (modem links, ISDN) to prevent fast bulk transfers from
disturbing interactive traffic like telnet too much.
NOTES
Since kernel release 2.2 there are no explicit interface statistics
for alias interfaces anymore. The statistics printed for the original
address are shared with all alias addresses on the same device. If you
want per-address statistics you should add explicit accounting rules
for the address using the ipchains(8) command.
Interrupt problems with Ethernet device drivers fail with EAGAIN. See
http://www.scyld.com/expert/irq-conflict.html for more information.
FILES
/proc/net/socket
/proc/net/dev
/proc/net/if_inet6
BUGS
While appletalk DDP and IPX addresses will be displayed they cannot be
altered by this command.
SEE ALSO
route(8), netstat(8), arp(8), rarp(8), ipchains(8)
AUTHORS
Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
Alan Cox, <Alan.Cox@linux.org>
Phil Blundell, <Philip.Blundell@pobox.com>
Andi Kleen
net-tools 14 August 2000 IFCONFIG(8)
