Section: Linux System Administrator's Manual (8)
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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,
displays the status of the currently active interfaces. If
argument is given, it displays the status of the given interface
only; if a single
argument 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
(AMPR Packet Radio),
(Appletalk Phase 2),
(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 if down
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
for the first Ethernet interface. If your kernel supports alias interfaces,
you can specify them with
for the first alias of eth0. You can use them to assign a second address. 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).
This flag causes the interface to be activated. It is implicitly
specified if an address is assigned to the interface.
This flag causes the driver for this interface to be shut down.
Enable or disable the use of the ARP protocol on this interface.
Enable or disable the
mode of the interface. If selected, all packets on the network will
be received by the interface.
Enable or disable
mode. If selected, all multicast packets on the network will be
received by the interface.
- 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
- 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
(twisted-pair 10Mbps Ethernet),
(external transceiver) and so on. The special medium type of
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
flag for the interface.
- [-]pointopoint [addr]
This keyword enables the
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
keyword does. Otherwise, set or clear the
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
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
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.
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), interfaces(5).
http://physics.nist.gov/cuu/Units/binary.html - 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>
- Address Families
- SEE ALSO
This document was created by
using the manual pages.
Time: 16:51:00 GMT, August 29, 2013