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       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 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  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 down

       -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 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/netmask  combination)  all  aliases  are  deleted,  if you delete the first

       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
              suppressed  when  using  the  IPv4  address as the kernel will use this to
              implicitly 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.

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

              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.

              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

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

              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 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


       route(8), netstat(8), arp(8), rarp(8), iptables(8), ifup(8), interfaces(5). - Prefixes for binary multiples


       Fred N. van Kempen, <>
       Alan Cox, <>
       Phil Blundell, <>
       Andi Kleen
       Bernd Eckenfels, <>