ifconfig - configure a network interface
ifconfig [-v] [-a] [-s] [interface]
ifconfig [-v] interface [aftype] options | address ...
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 currently
active interfaces. If a single interface
argument is given, it displays
the status of the given interface only; if a single -a
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
(TCP/IP, default), inet6
Packet Radio), ddp
(Appletalk Phase 2), ipx
(Novell IPX) and
(AMPR Packet radio). All numbers supplied as parts in IPv4
dotted decimal notation may be decimal, octal, or hexadecimal, as specified in
the ISO C standard (that is, a leading 0x or 0X implies hexadecimal;
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.
- display all interfaces which are currently available, even
- display a short list (like netstat -i)
- be more verbose for some error conditions
- The name of the interface. This is usually a driver name
followed 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
- This flag causes the interface to be activated. It is
implicitly 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 suppressed when
using the IPv4 0.0.0.0 address as the kernel will use this to implicitly
delete alias interfaces.
- This flag causes the driver for this interface to be shut
- Enable or disable the use of the ARP protocol on this
- 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 multicast packets on the network will be received by the
- mtu N
- This parameter sets the Maximum Transfer Unit (MTU) of an
- dstaddr addr
- Set the remote IP address for a point-to-point link (such
as PPP). This keyword is now obsolete; use the pointopoint keyword
- 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
- 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
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.
- [-]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
- 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
normally be needed as the drivers set the flag correctly themselves.
- The IP address to be assigned to this interface.
- txqueuelen length
- 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
Since net-tools 1.60-4 ifconfig is printing byte counters and human readable
counters with IEC 60027-2 units. So 1 KiB are 2^10 byte. Note, the numbers are
truncated to one decimal (which can by quite a large error if you consider 0.1
PiB is 112.589.990.684.262 bytes :)
Interrupt problems with Ethernet device drivers fail with EAGAIN
(SIOCSIIFLAGS: Resource temporarily unavailable)
it is most likely a
interrupt conflict. See http://www.scyld.com/expert/irq-conflict.html
for more information.
Ifconfig uses the ioctl access method to get the full address information, 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
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.
- Prefixes for binary multiples
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>