ifconfig - configure a network interface
ifconfig [-v] [-a] [-s] [interface]
ifconfig [-v] interface [aftype] options | address ...
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.
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.
- -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 syntax
like eth0:0 for the first alias of eth0. You can use them to assign
more addresses. 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; you can suppress this behavior
when using an alias interface by appending an - to the alias (e.g.
eth0:0-). It is also suppressed when using the IPv4 0.0.0.0 address
as the kernel will use this to implicitly delete alias interfaces.
- 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.
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.
Since net-tools 1.60-4 ifconfig is printing byte counters and
human readable counters with IEC 60027-2 units. So 1 KiB are 2^10 byte.
Note, the numbers are truncated to one decimal (which can by quite a large
error if you consider 0.1 PiB is 112.589.990.684.262 bytes :)
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.
/proc/net/dev
/proc/net/if_inet6
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.
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>