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IFCONFIG(8)		  BSD System Manager's Manual		   IFCONFIG(8)

NAME
     ifconfig — configure network interface parameters

SYNOPSIS
     ifconfig [-L] [-m] interface [create] [address_family]
	      [address[/prefixlength] [dest_address]] [parameters]
     ifconfig interface destroy
     ifconfig -a [-L] [-d] [-m] [-u] [address_family]
     ifconfig -l [-d] [-u] [address_family]
     ifconfig [-L] [-d] [-m] [-u]

DESCRIPTION
     Ifconfig is used to assign an address to a network interface and/or con‐
     figure network interface parameters.  Ifconfig must be used at boot time
     to define the network address of each interface present on a machine; it
     may also be used at a later time to redefine an interface's address or
     other operating parameters.

     The following options are available:

     address
	     For the DARPA-Internet family, the address is either a host name
	     present in the host name data base, hosts(5), or a DARPA Internet
	     address expressed in the Internet standard “dot notation”.

	     It is also possible to use the CIDR notation (also known as the
	     slash notation) to include the netmask.  That is, one can specify
	     an address like 192.168.0.1/16.

     address_family
	     Specify the address family which affects interpretation of the
	     remaining parameters.  Since an interface can receive transmis‐
	     sions in differing protocols with different naming schemes, spec‐
	     ifying the address family is recommended.	The address or proto‐
	     col families currently supported are “inet”, “inet6”,

     dest_address
	     Specify the address of the correspondent on the other end of a
	     point to point link.

     interface
	     This parameter is a string of the form “name unit”, for example,
	     “en0”.

     The following parameters may be set with ifconfig:

     add     Another name for the alias parameter.  Introduced for compatibil‐
	     ity with BSD/OS.

     alias   Establish an additional network address for this interface.  This
	     is sometimes useful when changing network numbers, and one wishes
	     to accept packets addressed to the old interface.	If the address
	     is on the same subnet as the first network address for this
	     interface, a netmask of 0xffffffff has to be specified.

     -alias  Remove the network address specified.  This would be used if you
	     incorrectly specified an alias, or it was no longer needed.  If
	     you have incorrectly set an NS address having the side effect of
	     specifying the host portion, removing all NS addresses will allow
	     you to respecify the host portion.

     anycast
	     (Inet6 only.)  Specify that the address configured is an anycast
	     address.  Based on the current specification, only routers may
	     configure anycast addresses.  Anycast address will not be used as
	     source address of any of outgoing IPv6 packets.

     arp     Enable the use of the Address Resolution Protocol (arp(4)) in
	     mapping between network level addresses and link level addresses
	     (default).	 This is currently implemented for mapping between
	     DARPA Internet addresses and IEEE 802 48-bit MAC addresses (Eth‐
	     ernet, FDDI, and Token Ring addresses).

     -arp    Disable the use of the Address Resolution Protocol (arp(4)).

     broadcast
	     (Inet only.)  Specify the address to use to represent broadcasts
	     to the network.  The default broadcast address is the address
	     with a host part of all 1's.

     debug   Enable driver dependent debugging code; usually, this turns on
	     extra console error logging.

     -debug  Disable driver dependent debugging code.

     delete  Another name for the -alias parameter.

     down    Mark an interface “down”.	When an interface is marked “down”,
	     the system will not attempt to transmit messages through that
	     interface.	 If possible, the interface will be reset to disable
	     reception as well.	 This action does not automatically disable
	     routes using the interface.

     ether   Another name for the lladdr parameter.

     lladdr addr
	     Set the link-level address on an interface.  This can be used to
	     e.g. set a new MAC address on an ethernet interface, though the
	     mechanism used is not ethernet-specific.  The address addr is
	     specified as a series of colon-separated hex digits.  If the
	     interface is already up when this option is used, it will be
	     briefly brought down and then brought back up again in order to
	     ensure that the receive filter in the underlying ethernet hard‐
	     ware is properly reprogrammed.

     media type
	     If the driver supports the media selection system, set the media
	     type of the interface to type.  Some interfaces support the mutu‐
	     ally exclusive use of one of several different physical media
	     connectors.  For example, a 10Mb/s Ethernet interface might sup‐
	     port the use of either AUI or twisted pair connectors.  Setting
	     the media type to “10base5/AUI” would change the currently active
	     connector to the AUI port.	 Setting it to “10baseT/UTP” would
	     activate twisted pair.  Refer to the interfaces' driver specific
	     documentation or man page for a complete list of the available
	     types.

     mediaopt opts
	     If the driver supports the media selection system, set the speci‐
	     fied media options on the interface.  The opts argument is a
	     comma delimited list of options to apply to the interface.	 Refer
	     to the interfaces' driver specific man page for a complete list
	     of available options.

     -mediaopt opts
	     If the driver supports the media selection system, disable the
	     specified media options on the interface.

     tunnel src_addr dest_addr
	     (IP tunnel devices only.)	Configure the physical source and des‐
	     tination address for IP tunnel interfaces (gif(4)).  The argu‐
	     ments src_addr and dest_addr are interpreted as the outer
	     source/destination for the encapsulating IPv4/IPv6 header.

     deletetunnel
	     Unconfigure the physical source and destination address for IP
	     tunnel interfaces previously configured with tunnel.

     create  Create the specified network pseudo-device.  If the interface is
	     given without a unit number, try to create a new device with an
	     arbitrary unit number.  If creation of an arbitrary device is
	     sucessful, the new device name is printed to standard output.

     destroy
	     Destroy the specified network pseudo-device.

     plumb   Another name for the create parameter.  Included for Solaris com‐
	     patibility.

     unplumb
	     Another name for the destroy parameter.  Included for Solaris
	     compatibility.

     metric n
	     Set the routing metric of the interface to n, default 0.  The
	     routing metric is used by the routing protocol (routed(8)).
	     Higher metrics have the effect of making a route less favorable;
	     metrics are counted as addition hops to the destination network
	     or host.

     mtu n   Set the maximum transmission unit of the interface to n, default
	     is interface specific.  The MTU is used to limit the size of
	     packets that are transmitted on an interface.  Not all interfaces
	     support setting the MTU, and some interfaces have range restric‐
	     tions.

     netmask mask
	     (Inet only.)  Specify how much of the address to reserve for sub‐
	     dividing networks into sub-networks.  The mask includes the net‐
	     work part of the local address and the subnet part, which is
	     taken from the host field of the address.	The mask can be speci‐
	     fied as a single hexadecimal number with a leading ‘0x’, with a
	     dot-notation Internet address, or with a pseudo-network name
	     listed in the network table networks(5).  The mask contains 1's
	     for the bit positions in the 32-bit address which are to be used
	     for the network and subnet parts, and 0's for the host part.  The
	     mask should contain at least the standard network portion, and
	     the subnet field should be contiguous with the network portion.

	     The netmask can also be specified in CIDR notation after the
	     address.  See the address option above for more information.

     prefixlen len
	     (Inet6 only.)  Specify that len bits are reserved for subdividing
	     networks into sub-networks.  The len must be integer, and for
	     syntactical reason it must be between 0 to 128.  It is almost
	     always 64 under the current IPv6 assignment rule.	If the parame‐
	     ter is omitted, 64 is used.

     remove  Another name for the -alias parameter.  Introduced for compati‐
	     bility with BSD/OS.

     link[0-2]
	     Enable special processing of the link level of the interface.
	     These three options are interface specific in actual effect, how‐
	     ever, they are in general used to select special modes of opera‐
	     tion.  An example of this is to enable SLIP compression, or to
	     select the connector type for some Ethernet cards.	 Refer to the
	     man page for the specific driver for more information.

     -link[0-2]
	     Disable special processing at the link level with the specified
	     interface.

     up	     Mark an interface “up”.  This may be used to enable an interface
	     after an “ifconfig down”.	It happens automatically when setting
	     the first address on an interface.	 If the interface was reset
	     when previously marked down, the hardware will be re-initialized.

     Ifconfig displays the current configuration for a network interface when
     no optional parameters are supplied.  If a protocol family is specified,
     ifconfig will report only the details specific to that protocol family.

     If the driver does supports the media selection system, the supported
     media list will be included in the output.

     If the -m flag is passed before an interface name, ifconfig will display
     all of the supported media for the specified interface.  If -L flag is
     supplied, address lifetime is displayed for IPv6 addresses, as time off‐
     set string.

     Optionally, the -a flag may be used instead of an interface name.	This
     flag instructs ifconfig to display information about all interfaces in
     the system.  The -d flag limits this to interfaces that are down, and -u
     limits this to interfaces that are up.  When no arguments are given, -a
     is implied.

     The -l flag may be used to list all available interfaces on the system,
     with no other additional information.  Use of this flag is mutually
     exclusive with all other flags and commands, except for -d (only list
     interfaces that are down) and -u (only list interfaces that are up).

     Only the super-user may modify the configuration of a network interface.

NOTES
     The media selection system is relatively new and only some drivers sup‐
     port it (or have need for it).

DIAGNOSTICS
     Messages indicating the specified interface does not exist, the requested
     address is unknown, or the user is not privileged and tried to alter an
     interface's configuration.

BUGS
     IPv6 link-local addresses are required for several basic communication
     between IPv6 node.	 If they are deleted by ifconfig manually, the kernel
     might show very strange behavior.	So, such manual deletions are strongly
     discouraged.

SEE ALSO
     netstat(1), netintro(4), rc(8), routed(8)

HISTORY
     The ifconfig command appeared in 4.2BSD.

BSD				 July 2, 2001				   BSD
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