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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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NAME | SYNOPSIS | DESCRIPTION | Address Families | OPTIONS | NOTES | FILES | BUGS | SEE ALSO | AUTHORS | COLOPHON |
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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 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 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 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 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.
-a display all interfaces which are currently available, even
if down
-s display a short list (like netstat -i)
-v be more verbose for some error conditions
interface
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 first (primary).
up 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.
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.
[-]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
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 pointopoint
keyword 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 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 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
normally be needed as the drivers set the flag correctly
themselves.
address
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.
name newname
Change the name of this interface to newname. The interface
must be shut down first.
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.
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.
/proc/net/dev
/proc/net/if_inet6
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 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),
interfaces(5)
http://physics.nist.gov/cuu/Units/binary.html - Prefixes for
binary multiples
Fred N. van Kempen, <[email protected]>
Alan Cox, <[email protected]>
Phil Blundell, <[email protected]>
Andi Kleen
Bernd Eckenfels, <[email protected]>
This page is part of the net-tools (networking utilities) project.
Information about the project can be found at
⟨http://net-tools.sourceforge.net/⟩. If you have a bug report for
this manual page, see ⟨http://net-tools.sourceforge.net/⟩. This
page was obtained from the project's upstream Git repository
⟨git://git.code.sf.net/p/net-tools/code⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-05-17.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
net-tools 2008-10-03 IFCONFIG(8)
Pages that refer to this page: getifaddrs(3), if_nameindex(3), if_nametoindex(3), sk98lin(4), wavelan(4), proc(5), proc_pid_net(5), arp(8), netstat(8), plipconfig(8), rarp(8), route(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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