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

   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.


   -a     display all interfaces which are currently  available,  even  if

   -s     display a short list (like netstat -i)

   -v     be more verbose for some error conditions

          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.

          Enable  or  disable  the  promiscuous mode of the interface.  If
          selected, all packets on the network will  be  received  by  the

          Enable   or   disable  all-multicast  mode.   If  selected,  all
          multicast packets  on  the  network  will  be  received  by  the

   mtu N  This  parameter  sets  the  Maximum  Transfer  Unit  (MTU) of an

   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

   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

   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).

          Set  the  multicast  flag  on  the  interface.  This  should not
          normally be  needed  as  the  drivers  set  the  flag  correctly

          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.

   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.




   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.


   route(8),   netstat(8),   arp(8),   rarp(8),   iptables(8),    ifup(8),
   http://physics.nist.gov/cuu/Units/binary.html  -  Prefixes  for  binary


   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>


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