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.\"     @(#)ifconfig.8	6.13 (Berkeley) 3/16/91
.\"
.Dd March 16, 1991
.Dt IFCONFIG 8
.Os BSD 4.2
.Sh NAME
.Nm ifconfig
.Nd configure network interface parameters
.Sh SYNOPSIS
.Nm ifconfig
.Ar interface address_family
.Oo
.Ar address
.Op Ar dest_address
.Oc
.Op Ar parameters
.Nm ifconfig
.Ar interface
.Op Ar protocol_family
.Sh DESCRIPTION
.Nm Ifconfig
is used to assign an address
to a network interface and/or configure
network interface parameters.
.Nm 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.
.Pp
Available operands for
.Nm ifconfig:
.Bl -tag -width Ds
.It Ar Address
For the
.Tn DARPA-Internet
family,
the address is either a host name present in the host name data
base, 
.Xr hosts 5 ,
or a
.Tn DARPA
Internet address expressed in the Internet standard
.Dq dot notation .
For the Xerox Network Systems(tm) family,
addresses are 
.Ar net:a.b.c.d.e.f ,
where
.Ar net
is the assigned network number (in decimal),
and each of the six bytes of the host number,
.Ar a
through
.Ar 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
.Tn 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 (carefully)
count out long strings of digits in network byte order.
.It Ar address_family
Specifies the
.Ar address family
which affects interpretation of the remaining parameters.
Since an interface can receive transmissions in differing protocols
with different naming schemes, specifying the address family is recommeded.
The address or protocol families currently
supported are
.Dq inet ,
.Dq iso ,
and
.Dq ns .
.It Ar Interface
The
.Ar interface
parameter is a string of the form
.Dq name unit ,
for example,
.Dq en0 
.El
.Pp
The following parameters may be set with 
.Nm ifconfig :
.Bl -tag -width dest_addressxx
.It Cm 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.
.It Cm arp
Enable the use of the Address Resolution Protocol in mapping
between network level addresses and link level addresses (default).
This is currently implemented for mapping between
.Tn DARPA
Internet
addresses and 10Mb/s Ethernet addresses.
.It Fl arp
Disable the use of the Address Resolution Protocol.
.It Cm 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.
.It Cm debug
Enable driver dependent debugging code; usually, this turns on
extra console error logging.
.It Fl debug
Disable driver dependent debugging code.
.It Cm 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.
.It Cm dest_address
Specify the address of the correspondent on the other end
of a point to point link.
.It Cm 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.
.It Cm 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 encapsulation of
.Tn CLNP
packets is done differently.
.It Cm metric Ar n
Set the routing metric of the interface to
.Ar n ,
default 0.
The routing metric is used by the routing protocol
.Pq Xr 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.
.It Cm netmask Ar mask
(Inet and Iso)
Specify how much of the address to reserve for subdividing
networks into sub-networks.
The mask includes the network part of the local address
and the subnet part, which is taken from the host field of the address.
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 network table
.Xr 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.
.\" see 
.\" Xr eon 5 .
.It Cm nsellength Ar n
.Pf ( Tn ISO
only)
This specifies a trailing number of bytes for a received
.Tn NSAP
used for local identification, the remaining leading part of which is
taken to be the
.Tn NET
(Network Entity Title).
The default value is 1, which is conformant to US
.Tn GOSIP .
When an iso address is set in an ifconfig command,
it is really the
.Tn NSAP
which is being specified.
For example, in
.Tn US GOSIP ,
20 hex digits should be
specified in the
.Tn ISO NSAP
to be assigned to the interface.
There is some evidence that a number different 1 may be useful
for
.Tn AFI
37 type addresses.
.It Cm trailers
Request the use of a ``trailer'' link level encapsulation when
sending (default).
If a network interface supports
.Cm 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 receiver.
On networks that support the Address Resolution Protocol (see
.Xr 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.
.It Fl trailers
Disable the use of a ``trailer'' link level encapsulation.
.It Cm 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.
.El
.Pp
.Pp
.Nm 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.
.Pp
Only the super-user may modify the configuration of a network interface.
.Sh DIAGNOSTICS
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.
.Sh SEE ALSO
.Xr netstat 1 ,
.Xr netintro 4 ,
.Xr rc 8 ,
.Xr routed 8 ,
.\" .Xr eon 5
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .