IFCONFIG(8) Linux System Administrator's Manual IFCONFIG(8)
ifconfig - configure a network interface
ifconfig [-v] [-a] [-s] [interface]
ifconfig [-v] interface [aftype] options | address ...
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
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.
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). All numbers supplied as parts in IPv4 dot-
ted decimal notation may be decimal, octal, or hexadecimal, as speci-
fied in the ISO C standard (that is, a leading 0x or 0X implies hexa-
decimal; otherwise, a leading '0' implies octal; otherwise, the number
is interpreted as decimal). Use of hexadecimal and octal numbers is not
RFC-compliant and therefore its use is discouraged.
-a display all interfaces which are currently available, even if
-s display a short list (like netstat -i)
-v be more verbose for some error conditions
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. If your kernel supports alias interfaces, you can
specify them with syntax like eth0:0 for the first alias of
eth0. You can use them to assign more addresses. To delete an
alias interface use ifconfig eth0:0 down. Note: for every scope
(i.e. same net with address/netmask combination) all aliases are
deleted, if you delete the first (primary).
up This flag causes the interface to be activated. It is implic-
itly specified if an address is assigned to the interface; you
can suppress this behavior when using an alias interface by
appending an - to the alias (e.g. eth0:0-). It is also sup-
pressed when using the IPv4 0.0.0.0 address as the kernel will
use this to implicitly delete alias interfaces.
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 interface.
Enable or disable the promiscuous mode of the interface. If
selected, all packets on the network will be received by the
Enable or disable all-multicast mode. If selected, all multi-
cast packets on the network will be received by the interface.
mtu N This parameter sets the Maximum Transfer Unit (MTU) of an inter-
Set the remote IP address for a point-to-point link (such as
PPP). This keyword is now obsolete; use the pointopoint keyword
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 an IPv6 address to an interface.
Remove an IPv6 address from an interface.
Create a new SIT (IPv6-in-IPv4) device, tunnelling to the given
Set the interrupt line used by this device. Not all devices can
dynamically change their IRQ setting.
Set the start address in I/O space for this device.
Set the start address for shared memory used by this device.
Only a few devices need this.
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 Ethernet),
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.
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.
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
Set the multicast flag on the interface. This should not nor-
mally be needed as the drivers set the flag correctly them-
The IP address to be assigned to this interface.
Set the length of the transmit queue of the device. It is useful
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.
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 iptables(8) command.
Interrupt problems with Ethernet device drivers fail with EAGAIN (SIOC-
SIIFLAGS: Resource temporarily unavailable) it is most likely a inter-
rupt conflict. See http://www.scyld.com/expert/irq-conflict.html for
Ifconfig uses the ioctl access method to get the full address informa-
tion, which limits hardware addresses to 8 bytes. Because Infiniband
hardware address has 20 bytes, only the first 8 bytes are displayed
correctly. Please use ip link command from iproute2 package to display
link layer informations including the hardware address.
While appletalk DDP and IPX addresses will be displayed they cannot be
altered by this command.
route(8), netstat(8), arp(8), rarp(8), iptables(8), ifup(8), inter-
http://physics.nist.gov/cuu/Units/binary.html - Prefixes for binary
Fred N. van Kempen, <firstname.lastname@example.org>
Alan Cox, <Alan.Cox@linux.org>
Phil Blundell, <Philip.Blundell@pobox.com>
Bernd Eckenfels, <email@example.com>
net-tools 2008-10-03 IFCONFIG(8)
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