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IFCONFIG(8)                    Linux System Administrator's Manual                    IFCONFIG(8)



NAME
       ifconfig - configure a network interface

SYNOPSIS
       ifconfig [-v] [-a] [-s] [interface]
       ifconfig [-v] 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       This  program is obsolete!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 debug-
       ging 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 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 num-
              ber, 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 combina-
              tion) 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  Ether-
              net), 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.

       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.

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
       ip(8), iptables(8)
       http://physics.nist.gov/cuu/Units/binary.html - Prefixes for binary multiples

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
       Bernd Eckenfels, <net-tools AT lina.de>



net-tools                                   2008-10-03                                IFCONFIG(8)

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