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IFCONFIG(8) Linux System Administrator's Manual IFCONFIG(8)
NAME
ifconfig - configure a network interface
SYNOPSIS
ifconfig [-v] [-a] [-s] [interface]
ifconfig [-v] 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 debug-
ging or when system tuning is needed.
If no arguments are given, ifconfig displays the status of the currently active inter-
faces. If a single interface argument is given, it displays the status of the given in-
terface 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.
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 ad-
dresses. 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.
OPTIONS
-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 num-
ber, 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/net-
mask 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 sup-
pressed when using the IPv4 0.0.0.0 address as the kernel will use this to implic-
itly 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 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 in-
terface. 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 op-
eration. 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.
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 ad-
dresses on the same device. If you want per-address statistics you should add explicit ac-
counting rules for the address using the iptables(8) command.
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.
FILES
/proc/net/dev
/proc/net/if_inet6
BUGS
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.
SEE ALSO
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
AUTHORS
Fred N. van Kempen, <waltje AT uwalt.org>
Alan Cox, <Alan.Cox AT linux.org>
Phil Blundell, <Philip.Blundell AT pobox.com>
Andi Kleen
Bernd Eckenfels, <net-tools AT lina.de>
net-tools 2008-10-03 IFCONFIG(8)
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