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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 ...

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  in-
       terface  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 ad-
       dresses.  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 syntax like eth0:0 for the first  alias
              of  eth0.  You  can use them to assign more addresses. To delete an alias interface
              use ifconfig eth0:0 down.  Note: for every scope (i.e. same net  with  address/net-
              mask 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; you can suppress this behavior when using  an
              alias  interface  by  appending an - to the alias (e.g.  eth0:0-).  It is also sup-
              pressed when using the IPv4 0.0.0.0 address as the kernel will use this to  implic-
              itly delete alias interfaces.

       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 in-
              terface.  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 op-
              eration.  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 ad-
       dresses on the same device. If you want per-address statistics you should add explicit ac-
       counting 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.

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
       route(8), netstat(8), arp(8), rarp(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                                   2008-10-03                                IFCONFIG(8)

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