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

     ifconfig - configure network interface parameters

     ifconfig interface address_family [address [dest_address]] [parameters]
     ifconfig interface [protocol_family]

     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.

     Available operands for ifconfig:

             For the DARPA-Internet family, the address is either a host name
             present in the host name data base, hosts(5),  or a DARPA Inter-
             net address expressed in the Internet standard ``dot notation''.
             For the Xerox Network Systems(tm) family, addresses are
             net:a.b.c.d.e.f, where net is the assigned network number (in
             decimal), and each of the six bytes of the host number, a through
             f, are specified in hexadecimal.  The host number may be omitted
             on 10Mb/s Ethernet interfaces, which use the hardware physical
             address, and on interfaces other than the first.  For the ISO
             family, addresses are specified as a long hexadecimal string, as
             in the Xerox family.  However, two consecutive dots imply a zero
             byte, and the dots are optional, if the user wishes to (careful-
             ly) count out long strings of digits in network byte order.

             Specifies 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 recommeded.  The address or protocol
             families currently supported are ``inet'', ``iso'', and ``ns''.

             The interface parameter is a string of the form ``name unit'',
             for example, ``en0''

     The following parameters may be set with ifconfig:

     alias           Establish an additional network address for this inter-
                     face.  This is sometimes useful when changing network
                     numbers, and one wishes to accept packets addressed to
                     the old interface.

     arp             Enable the use of the Address Resolution Protocol in map-
                     ping between network level addresses and link level ad-
                     dresses (default).  This is currently implemented for
                     mapping between DARPA Internet addresses and 10Mb/s Eth-
                     ernet addresses.

     -arp            Disable the use of the Address Resolution Protocol.

     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          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.

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

     down            Mark an interface ``down''.  When an interface is marked
                     ``down'', the system will not attempt to transmit mes-
                     sages through that interface.  If possible, the interface
                     will be reset to disable reception as well.  This action
                     does not automatically disable routes using the inter-

     ipdst           This is used to specify an Internet host who is willing
                     to receive ip packets encapsulating NS packets bound for
                     a remote network.  An apparent point to point link is
                     constructed, and the address specified will be taken as
                     the NS address and network of the destination.  IP encap-
                     sulation of CLNP packets is done differently.

     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.

     netmask mask    (Inet and ISO) Specify how much of the address to reserve
                     for subdividing networks into sub-networks.  The mask in-
                     cludes the network part of the local address and the sub-
                     net part, which is taken from the host field of the ad-
                     dress.  The mask can be specified as a single hexadecimal
                     number with a leading 0x, with a dot-notation Internet
                     address, or with a pseudo-network name listed in the net-
                     work 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 net-
                     work portion, and the subnet field should be contiguous
                     with the network portion.

     nsellength n    (ISO only) This specifies a trailing number of bytes for
                     a received NSAP used for local identification, the re-
                     maining leading part of which is taken to be the NET
                     (Network Entity Title).  The default value is 1, which is
                     conformant to US GOSIP. When an ISO address is set in an
                     ifconfig command, it is really the NSAP which is being
                     specified.  For example, in US GOSIP, 20 hex digits
                     should be specified in the ISO NSAP to be assigned to the
                     interface.  There is some evidence that a number differ-
                     ent from 1 may be useful for AFI 37 type addresses.

     trailers        Request the use of a ``trailer'' link level encapsulation
                     when sending (default).  If a network interface supports
                     trailers, the system will, when possible, encapsulate
                     outgoing messages in a manner which minimizes the number
                     of memory to memory copy operations performed by the re-
                     ceiver.  On networks that support the Address Resolution
                     Protocol (see arp(4);  currently, only 10 Mb/s Ethernet),
                     this flag indicates that the system should request that
                     other systems use trailers when sending to this host.
                     Similarly, trailer encapsulations will be sent to other
                     hosts that have made such requests.  Currently used by
                     Internet protocols only.

     -trailers       Disable the use of a ``trailer'' link level encapsula-

     link[0-2]       Enable special processing of the link level of the inter-
                     face.  These three options are interface specific in ac-
                     tual effect, however, they are in general used to select
                     special modes of operation. An example of this is to en-
                     able SLIP compression. Currently, only used by SLIP.

     -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 auto-
                     matically 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.

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

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

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

     The ifconfig command appeared in 4.2BSD.

4.2 Berkeley Distribution        June 1, 1994                                3