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 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 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 number, for example eth0 for the first
Ethernet interface. If your kernel supports alias interfaces,
you can specify them with eth0:0 for the first alias of eth0.
You can use them to assign a second address. To delete an alias
interface use ifconfig eth0:0 down. Note: for every scope (i.e.
same net with address/netmask 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.
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 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 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@uwalt.nl.mugnet.org>
Alan Cox, <Alan.Cox@linux.org>
Phil Blundell, <Philip.Blundell@pobox.com>
Andi Kleen
Bernd Eckenfels, <net-tools@lina.inka.de>
Free and Open Source Software