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IFCONFIG(8) Linux Programmer's Manual IFCONFIG(8)

NAME
ifconfig - configure a network interface

SYNOPSIS
ifconfig [interface]
ifconfig interface [aftype] options | address ...

NOTE
This program is obsolete! For replacement check ip addr and ip link. For statistics use ip -s link.

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 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 argu-
ment is given, it displays the status of the given interface only; if a single -a argument is given, it displays the sta-
tus 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 fam-
ily 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 hexamedial and octal numbers is not RFC-compliant and therefore
its use is discouraged and may go away.

OPTIONS
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.

up This flag causes the interface to be activated. It is implicitly specified if an address is assigned to the
interface.

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.

metric N
This parameter sets the interface metric. It is not available under GNU/Linux.

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 pointo-
point 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 obso-
lete 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.

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 addresses on the same device. If you want per-address statistics you
should add explicit accounting rules for the address using the ipchains(8) command.

Interrupt problems with Ethernet device drivers fail with EAGAIN. See http://www.scyld.com/expert/irq-conflict.html for
more information.

FILES
/proc/net/socket
/proc/net/dev
/proc/net/if_inet6

BUGS
Ifconfig uses obsolete kernel interface. It uses the ioctl access method to get the full address information, which lim-
its hardware addresses to 8 bytes. Since an Infiniband address is 20 bytes, only the first 8 bytes of Infiniband address
are displayed.

While appletalk DDP and IPX addresses will be displayed they cannot be altered by this command.