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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 ...


NOTE
       This  program is obsolete!  For replacement check ip addr and ip link.  For statis-
       tics 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 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 sup-
       ported 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 lead-
       ing '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 discour-
       aged and may go away.


OPTIONS
       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.

       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.

       metric N
              This parameter  sets  the  interface  metric.  It  is  not  available  under
              GNU/Linux.

       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 tel-
              net 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
       Ifconfig uses obsolete kernel interface.  It uses the ioctl access  method  to  get
       the full address information, which limits hardware addresses to 8 bytes.  Since an
       Infiniband address is 20 bytes, only the first 8 bytes of  Infiniband  address  are
       displayed.

       While  appletalk  DDP and IPX addresses will be displayed they cannot be altered by
       this command.


SEE ALSO
       ip(8)


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



net-tools                       14 August 2000                     IFCONFIG(8)

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