ifconfig

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  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 de-
       coding and displaying all protocol addresses.  Currently supported  ad-
       dress 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 dec-
       imal 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 inter-
       preted  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 fol-
              lowed 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 (primary).

       up     This flag causes the interface to be activated.  It  is  implic-
              itly  specified  if an address is assigned to the interface; you
              can suppress this behavior when using an alias interface by  ap-
              pending  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 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.

       [-]promisc
              Enable or disable the promiscuous mode of the interface.  If se-
              lected, all packets on the network will be received by  the  in-
              terface.

       [-]allmulti
              Enable  or  disable all-multicast mode.  If selected, all multi-
              cast packets on the network will be received by the interface.

       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 ad-
              dress  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 no-
              body 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  in-
              clude  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 la-
              tency (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  ad-
       dress  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 (SIOC-
       SIIFLAGS: Resource temporarily unavailable) it is most likely a  inter-
       rupt  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  informa-
       tion,  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), inter-
       faces(5).
       http://physics.nist.gov/cuu/Units/binary.html  -  Prefixes  for  binary
       multiples

AUTHORS
       Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
       Alan Cox, <Alan.Cox@linux.org>
       Phil Blundell, <Philip.Blundell@pobox.com>
       Andi Kleen
       Bernd Eckenfels, <net-tools@lina.inka.de>

net-tools                         2008-10-03                       IFCONFIG(8)