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IFCONFIG(8)		   Linux Programmer's Manual		   IFCONFIG(8)



NAME
       ifconfig - configure a network interface

SYNOPSIS
       ifconfig [interface]
       ifconfig 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  cur-
       rently  active interfaces.  If a single interface argument is given, it
       displays the status of the given interface only; if a single  -a	 argu-
       ment  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 dot-
       ted decimal notation may be decimal, octal, or hexadecimal,  as	speci-
       fied  in	 the  ISO C standard (that is, a leading 0x or 0X implies hex-
       adecimal; 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  fol-
	      lowed  by a unit number, for example eth0 for the first Ethernet
	      interface.

       up     This flag causes the interface to be activated.  It  is  implic-
	      itly 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 multi-
	      cast packets on the network will be received by the interface.

       metric N
	      This parameter sets the interface metric.

       mtu N  This parameter sets the Maximum Transfer Unit (MTU) of an inter-
	      face.

       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  nor-
	      mally  be	 needed	 as  the  drivers set the flag correctly them-
	      selves.

       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
       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), ipchains(8)

AUTHORS
       Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
       Alan Cox, <Alan.Cox@linux.org>
       Phil Blundell, <Philip.Blundell@pobox.com>
       Andi Kleen



net-tools			14 August 2000			   IFCONFIG(8)
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