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IFCONFIG


Section: Linux Programmer’s Manual (8)
Updated: 14 August 2000
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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This program is obsolete!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

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 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 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
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.



 

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 limits 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.


 

SEE ALSO

ip(8)


 

AUTHORS

Fred N. van Kempen, <[email protected]>

Alan Cox, <[email protected]>

Phil Blundell, <[email protected]>

Andi Kleen



 

Index



NAME

SYNOPSIS

NOTE

DESCRIPTION

Address Families

OPTIONS

NOTES

FILES

BUGS

SEE ALSO

AUTHORS



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