man--ifconfig
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This program is obsolete!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 inter-
faces. 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 inter-
faces, 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 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 key-
word 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 cur-
rently 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 pre-
vent 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 inter-
faces 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 limits hardware addresses to 8 bytes. Since an
Infiniband address is 20 bytes, only the first 8 bytes of Infiniband address are dis-
played.
While appletalk DDP and IPX addresses will be displayed they cannot be altered by this
command.
SEE ALSO
ip(8)
AUTHORS
Fred N. van Kempen, <[email protected]>
Alan Cox, <[email protected]>
Phil Blundell, <[email protected]>
Andi Kleen
net-tools 14 August 2000 IFCONFIG(8)
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