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 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; oth‐
       erwise, 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 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 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 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 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 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_POINTO‐
              POINT 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  trans‐
              fers 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 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/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@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)