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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 ...
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 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.
Address Families
If the first argument after the interface name is recognized as the name of a sup-
ported 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 lead-
ing '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 discour-
aged 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.
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 tel-
net 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
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), ipchains(8)
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
net-tools 14 August 2000 IFCONFIG(8)
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