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ifconfig command man page

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

       ifconfig - configure a network interface
       ifconfig [interface]
       ifconfig 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

       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
       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 dot-
       ted decimal notation may be decimal, octal, or hexadecimal,  as speci-
       fied  in the  ISO C standard (that is, a leading 0x or 0X implies hex-
       adecimal; otherwise, a leading ’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 discouraged and may go away.

     The name of the interface.  This is usually a driver  name  fol-
     lowed  by a unit number, for example eth0 for the first Ethernet

       up     This flag causes the interface to be activated.  It  is  implic-
     itly 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.

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

     Enable  or  disable all-multicast mode.  If selected, all multi-
     cast 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 inter-

       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

       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

       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).

     Set the multicast flag on the interface. This  should  not  nor-
     mally  be needed as  the  drivers set the flag correctly them-

     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 ipchains(8) command.

       Interrupt  problems  with Ethernet device drivers fail with EAGAIN. See for more information.


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

       route(8), netstat(8), arp(8), rarp(8), ipchains(8)

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

net-tools 14 August 2000   IFCONFIG(8)


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