.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)ifconfig.8c	6.4 (Berkeley) 5/22/86
.\"
.TH IFCONFIG 8C "May 22, 1986"
.UC 5
.SH NAME
ifconfig \- configure network interface parameters
.SH SYOPNSIS
.B /etc/ifconfig
interface address_family
[
.I address
[
.I dest_address
] ] [
.I parameters
]
.br
.B /etc/ifconfig
interface
[
protocol_family
]
.SH DESCRIPTION
.I Ifconfig
is used to assign an address
to a network interface and/or configure
network interface parameters.
.I 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
.I interface
parameter is a string of the form ``name unit'', e.g. ``en0''.
.LP
Since an interface may receive transmissions in differing protocols,
each of which may require separate naming schemes, it is necessary
to specify the
.IR address_family ,
which may change the interpretation of the remaining parameters.
The address families currently supported are ``inet'' and ``ns''.
.LP
For the DARPA-Internet family,
the address is either a host name present in the host name data
base, 
.IR hosts (5),
or a DARPA Internet address expressed in the Internet standard
``dot notation''.
For the Xerox Network Systems(tm) family,
addresses are 
.IR net:a.b.c.d.e.f ,
where
.I net
is the assigned network number (in decimal),
and each of the six bytes of the host number,
.I a
through
.IR 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.
.PP
The following parameters may be set with 
.IR ifconfig :
.TP 15
.B 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.
.TP 15
.B 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.
.TP 15
.B trailers
Request the use of a ``trailer'' link level encapsulation when
sending (default).
If a network interface supports
.IR 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
.IR arp (4P);
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.
.TP 15
.B \-trailers
Disable the use of a ``trailer'' link level encapsulation.
.TP 15
.B 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 DARPA Internet
addresses and 10Mb/s Ethernet addresses.
.TP 15
.B \-arp
Disable the use of the Address Resolution Protocol.
.TP 15
.BI metric " n"
Set the routing metric of the interface to
.IR n ,
default 0.
The routing metric is used by the routing protocol
.RI ( routed (8c)).
Higher metrics have the effect of making a route
less favorable; metrics are counted as addition hops
to the destination network or host.
.TP 15
.B debug
Enable driver dependent debugging code; usually, this turns on
extra console error logging.
.TP 15
.B \-debug
Disable driver dependent debugging code.
.TP 15
.BI netmask " mask"
(Inet only)
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
.IR 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.
.TP 15
.B dstaddr
Specify the address of the correspondent on the other end
of a point to point link.
.TP 15
.B 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.
.TP 15
.B ipdst
(NS only)
This is used to specify an Internet host who is willing to receive
ip packets encapsulating NS packets bound for a remote network.
In this case, an apparent point to point link is constructed, and
the address specified will be taken as the NS address and network
of the destinee.
.PP
.I 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"
netstat(1), intro(4N), rc(8)