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



NAME
       ifconfig - configure a network interface

SYNOPSIS
       ifconfig [-v] [-a] [-s] [interface]
       ifconfig [-v] 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 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).

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.

       metric N
              This parameter sets the interface metric.

       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 ipchains(8) or 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/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), iptables(8), ifup(8), interfaces(5).
       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                                   2007-12-02                                IFCONFIG(8)