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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 exam-
             ple, ``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 inter-
             face 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-ini-
             tialized.

     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