.\"	$NetBSD: ifconfig.8,v 1.111 2016/09/11 22:10:47 sevan Exp $
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.\"     @(#)ifconfig.8	8.4 (Berkeley) 6/1/94
.\"
.Dd January 7, 2016.
.Dt IFCONFIG 8
.Os
.Sh NAME
.Nm ifconfig
.Nd configure network interface parameters
.Sh SYNOPSIS
.Nm
.Op Fl N
.Ar interface address_family
.Oo
.Ar address
.Op Ar dest_address
.Oc
.Op Ar parameters
.Nm
.Op Fl hLmNvz
.Ar interface
.Op Ar protocol_family
.Nm
.Fl a
.Op Fl bdhLNmsuvz
.Op Ar protocol_family
.Nm
.Fl l
.Op Fl bdsu
.Nm
.Fl s
.Ar interface
.Nm
.Fl w
.Ar secs
.Op Fl W Ar secs
.Nm
.Fl C
.Sh DESCRIPTION
.Nm
is used to assign an address
to a network interface and/or configure
network interface parameters.
.Nm
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 :
.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
.Pq 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 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
.Pq 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 recommended.
The address or protocol families currently
supported are
.Dq inet ,
.Dq inet6 ,
.Dq atalk ,
.Dq iso ,
and
.Dq link .
.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 :
.Bl -tag -width dest_addressxx
.It Cm active
This keyword applies when
.Nm
adds or modifies any link-layer address.
It indicates that
.Nm
should
.Dq activate
the address.
Activation makes an address the default source for transmissions
on the interface.
You may not delete the active address from an interface.
You must activate some other address, first.
.It Cm advbase Ar n
If the driver is a
.Xr carp 4
pseudo-device, set the base advertisement interval to
.Ar n
seconds.
This ia an 8-bit number; the default value is 1 second.
.It Cm advskew Ar n
If the driver is a
.Xr carp 4
pseudo-device, skew the advertisement interval by
.Ar n .
This is an 8-bit number; the default value is 0.
.Pp
Taken together the
.Cm advbase
indicate how frequently, in seconds, the host will advertise the fact that it
considers itself the master of the virtual host.
The formula is
.Cm advbase
+
.Pf ( Cm advskew
/ 256).
If the master does not advertise within three times this interval, this host
will begin advertising as master.
.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 Fl alias
Remove the specified network address alias.
.It Cm arp
Enable the use of the Address Resolution Protocol in mapping
between network level addresses and link level addresses
.Pq default .
This is currently implemented for mapping between
.Tn DARPA
Internet
addresses and Ethernet addresses.
.It Fl arp
Disable the use of the Address Resolution Protocol.
.It Cm anycast
.Pq inet6 only
Set the IPv6 anycast address bit.
.It Fl anycast
.Pq inet6 only
Clear the IPv6 anycast address bit.
.It Cm broadcast Ar mask
.Pq 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 carpdev Ar iface
If the driver is a
.Xr carp 4
pseudo-device, attach it to
.Ar iface .
If not specified, the kernel will attempt to select an interface with
a subnet matching that of the carp interface.
.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.
.Cm delete
does not work for IPv6 addresses.
Use
.Fl alias
with explicit IPv6 address instead.
.It Ar 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 media Ar type
Set the media type of the interface to
.Ar type .
Some interfaces support the mutually exclusive use of one of several
different physical media connectors.
For example, a 10Mb/s Ethernet
interface might support the use of either
.Tn AUI
or twisted pair connectors.
Setting the media type to
.Dq 10base5
or
.Dq AUI
would change the currently active connector to the AUI port.
Setting it to
.Dq 10baseT
or
.Dq UTP
would activate twisted pair.
Refer to the interfaces' driver
specific man page for a complete list of the available types
and the
.Xr ifmedia 4
manual page for a list of media types.
See the
.Fl m
flag below.
.It Cm mediaopt Ar opts
Set the specified media options on the interface.
.Ar opts
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.
Also see the
.Xr ifmedia 4
manual page for a list of media options.
.It Fl mediaopt Ar opts
Disable the specified media options on the interface.
.It Cm mode Ar mode
If the driver supports the media selection system, set the specified
operating mode on the interface to
.Ar mode .
For IEEE 802.11 wireless interfaces that support multiple operating modes
this directive is used to select between 802.11a
.Pq Dq 11a ,
802.11b
.Pq Dq 11b ,
and 802.11g
.Pq Dq 11g
operating modes.
.It Cm instance Ar minst
Set the media instance to
.Ar minst .
This is useful for devices which have multiple physical layer interfaces
.Pq PHYs .
Setting the instance on such devices may not be strictly required
by the network interface driver as the driver may take care of this
automatically; see the driver's manual page for more information.
.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 mtu Ar n
Set the maximum transmission unit of the interface to
.Ar n .
Most interfaces do not support this option.
.It Cm netmask Ar mask
.Pq inet, inet6, 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.
.Pp
For INET and INET6 addresses, the netmask can also be given with
slash-notation after the address
.Pq e.g 192.168.17.3/24 .
.\" 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
.Pq 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 from 1 may be useful
for
.Tn AFI
37 type addresses.
.It Cm state Ar state
Explicitly force the
.Xr carp 4
pseudo-device to enter this state.
Valid states are
.Ar init ,
.Ar backup ,
and
.Ar master .
.It Cm frag Ar threshold
.Pq IEEE 802.11 devices only
Configure the fragmentation threshold for IEEE 802.11-based wireless
network interfaces.
.It Cm rts Ar threshold
.Pq IEEE 802.11 devices only
Configure the RTS/CTS threshold for IEEE 802.11-based wireless
network interfaces.
This controls the number of bytes used for the RTS/CTS handshake boundary.
The
.Ar threshold
can be any value between 0 and 2347.
The default is 2347, which indicates the RTS/CTS mechanism should not be used.
.It Cm ssid Ar id
.Pq IEEE 802.11 devices only
Configure the Service Set Identifier (aka the network name)
for IEEE 802.11-based wireless network interfaces.
The
.Ar id
can either be any text string up to 32 characters in length,
or a series of up to 64 hexadecimal digits preceded by
.Dq 0x .
Setting
.Ar id
to the empty string allows the interface to connect to any available
access point.
.It Cm nwid Ar id
Synonym for
.Dq ssid .
.It Cm hidessid
.Pq IEEE 802.11 devices only
When operating as an access point, do not broadcast the SSID
in beacon frames or respond to probe request frames unless
they are directed to the ap (i.e., they include the ap's SSID).
By default, the SSID is included in beacon frames and
undirected probe request frames are answered.
.It Fl hidessid
.Pq IEEE 802.11 devices only
When operating as an access point, broadcast the SSID
in beacon frames and answer and respond to undirected probe
request frames (default).
.It Cm nwkey Ar key
.Pq IEEE 802.11 devices only
Enable WEP encryption for IEEE 802.11-based wireless network interfaces
with the
.Ar key .
The
.Ar key
can either be a string, a series of hexadecimal digits preceded by
.Dq 0x ,
or a set of keys in the form
.Ar n:k1,k2,k3,k4 ,
where
.Ar n
specifies which of keys will be used for all transmitted packets,
and four keys,
.Ar k1
through
.Ar k4 ,
are configured as WEP keys.
Note that the order must be match within same network if multiple keys
are used.
For IEEE 802.11 wireless network, the length of each key is restricted to
40 bits, i.e., 5-character string or 10 hexadecimal digits,
while the WaveLAN/IEEE Gold cards accept the 104 bits
.Pq 13 characters
key.
.It Cm nwkey Cm persist
.Pq IEEE 802.11 devices only
Enable WEP encryption for IEEE 802.11-based wireless network interfaces
with the persistent key written in the network card.
.It Cm nwkey Cm persist: Ns Ar key
.Pq IEEE 802.11 devices only
Write the
.Ar key
to the persistent memory of the network card, and
enable WEP encryption for IEEE 802.11-based wireless network interfaces
with the
.Ar key .
.It Fl nwkey
.Pq IEEE 802.11 devices only
Disable WEP encryption for IEEE 802.11-based wireless network interfaces.
.It Cm apbridge
.Pq IEEE 802.11 devices only
When operating as an access point, pass packets between
wireless clients directly (default).
.It Fl apbridge
.Pq IEEE 802.11 devices only
When operating as an access point, pass packets through
the system so that they can be forwared using some other mechanism.
Disabling the internal bridging is useful when traffic
is to be processed with packet filtering.
.It Cm pass Ar passphrase
If the driver is a
.Xr carp 4
pseudo-device, set the authentication key to
.Ar passphrase .
There is no passphrase by default
.It Cm powersave
.Pq IEEE 802.11 devices only
Enable 802.11 power saving mode.
.It Fl powersave
.Pq IEEE 802.11 devices only
Disable 802.11 power saving mode.
.It Cm powersavesleep Ar duration
.Pq IEEE 802.11 devices only
Set the receiver sleep duration in milliseconds for 802.11 power saving mode.
.It Cm bssid Ar bssid
.Pq IEEE 802.11 devices only
Set the desired BSSID for IEEE 802.11-based wireless network interfaces.
.It Fl bssid
.Pq IEEE 802.11 devices only
Unset the desired BSSID for IEEE 802.11-based wireless network interfaces.
The interface will automatically select a BSSID in this mode, which is
the default.
.It Cm chan Ar chan
.Pq IEEE 802.11 devices only
Select the channel
.Pq radio frequency
to be used for IEEE 802.11-based wireless network interfaces.
.It Fl chan
.Pq IEEE 802.11 devices only
Unset the desired channel to be used
for IEEE 802.11-based wireless network interfaces.
It does not affect the channel to be created for IBSS or hostap mode.
.It Cm list scan
.Pq IEEE 802.11 devices only
Display the access points and/or ad-hoc neighbors
located in the vicinity.
The
.Fl v
flag may be used to display long SSIDs.
.Fl v
also causes received information elements to be displayed symbolically.
The interface must be up before any scanning operation.
Only the super-user can use this command.
.It Cm tunnel Ar src_addr Ns Oo Ar ,src_port Oc Ar dest_addr Ns Oo Ar ,dest_port
.Oc
.Pq IP tunnel devices only
Configure the physical source and destination address for IP tunnel
interfaces, including
.Xr gif 4 .
The arguments
.Ar src_addr
and
.Ar dest_addr
are interpreted as the outer source/destination for the encapsulating
IPv4/IPv6 header.
.Pp
On a
.Xr gre 4
interface in UDP mode, the arguments
.Ar src_port
and
.Ar dest_port
are interpreted as the outer source/destination port for the encapsulating
UDP header.
.It Cm deletetunnel
Unconfigure the physical source and destination address for IP tunnel
interfaces previously configured with
.Cm tunnel .
.It Cm create
Create the specified network pseudo-device.
.It Cm destroy
Destroy the specified network pseudo-device.
.It Cm pltime Ar n
.Pq inet6 only
Set preferred lifetime for the address.
.It Cm prefixlen Ar n
.Pq inet and inet6 only
Effect is similar to
.Cm netmask .
but you can specify by prefix length by digits.
.It Cm deprecated
.Pq inet6 only
Set the IPv6 deprecated address bit.
.It Fl deprecated
.Pq inet6 only
Clear the IPv6 deprecated address bit.
.It Cm eui64
.Pq inet6 only
Fill interface index
.Pq lowermost 64bit of an IPv6 address
automatically.
.It Cm link[0-2]
Enable special processing of the link level of the interface.
These three options are interface specific in actual effect, however,
they are in general used to select special modes of operation.
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.
.It Fl link[0-2]
Disable special processing at the link level with the specified interface.
.It Cm linkstr
Set a link-level string parameter for the interface.
This functionality varies from interface to interface.
Refer to the man page for the specific driver
for more information.
.It Fl linkstr
Remove an interface link-level string parameter.
.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.
.It Cm vhid Ar n
If the driver is a
.Xr carp 4
pseudo-device, set the virtual host ID to
.Ar n .
Acceptable values are 1 to 255.
.It Cm vlan Ar vid
If the interface is a
.Xr vlan 4
pseudo-interface, set the VLAN identifier to
.Ar vid .
These are the first 12 bits (0-4095) from a 16-bit integer used
to create an 802.1Q VLAN header for packets sent from the
.Xr vlan 4
interface.
Note that
.Cm vlan
and
.Cm vlanif
must be set at the same time.
.It Cm vlanif Ar iface
If the interface is a
.Xr vlan 4
pseudo-interface, associate the physical interface
.Ar iface
with it.
Packets transmitted through the
.Xr vlan 4
interface will be diverted to the specified physical interface
.Ar iface
with 802.1Q VLAN encapsulation.
Packets with 802.1Q encapsulation received
by the physical interface with the correct VLAN tag will be diverted to the
associated
.Xr vlan 4
pseudo-interface.
The VLAN interface is assigned a copy of the physical
interface's flags and
.Tn Ethernet
address.
If the
.Xr vlan 4
interface already has a physical interface associated with it, this command
will fail.
To change the association to another physical interface, the
existing association must be cleared first.
Note that
.Cm vlanif
and
.Cm vlan
must be set at the same time.
.It Cm -vlanif Ar iface
Dissociate
.Ar iface
from the
.Xr vlan 4
interface.
.It Cm agrport Ar iface
Add
.Ar iface
to the
.Xr agr 4
interface.
.It Cm -agrport Ar iface
Remove
.Ar iface
from the
.Xr agr 4
interface.
.It Cm vltime Ar n
.Pq inet6 only
Set valid lifetime for the address.
.It Cm ip4csum
Shorthand of
.Dq ip4csum-tx ip4csum-rx
.It Cm -ip4csum
Shorthand of
.Dq -ip4csum-tx -ip4csum-rx
.It Cm tcp4csum
Shorthand of
.Dq tcp4csum-tx tcp4csum-rx
.It Cm -tcp4csum
Shorthand of
.Dq -tcp4csum-tx -tcp4csum-rx
.It Cm udp4csum
Shorthand of
.Dq udp4csum-tx udp4csum-rx
.It Cm -udp4csum
Shorthand of
.Dq -udp4csum-tx -udp4csum-rx
.It Cm tcp6csum
Shorthand of
.Dq tcp6csum-tx tcp6csum-rx
.It Cm -tcp6csum
Shorthand of
.Dq -tcp6csum-tx -tcp6csum-rx
.It Cm udp6csum
Shorthand of
.Dq udp6csum-tx udp6csum-rx
.It Cm -udp6csum
Shorthand of
.Dq -udp6csum-tx -udp6csum-rx
.It Cm ip4csum-tx
Enable hardware-assisted IPv4 header checksums for the out-bound direction.
.It Cm -ip4csum-tx
Disable hardware-assisted IPv4 header checksums for the out-bound direction.
.It Cm ip4csum-rx
Enable hardware-assisted IPv4 header checksums for the in-bound direction.
.It Cm -ip4csum-rx
Disable hardware-assisted IPv4 header checksums for the in-bound direction.
.It Cm tcp4csum-tx
Enable hardware-assisted TCP/IPv4 checksums for the out-bound direction.
.It Cm -tcp4csum-tx
Disable hardware-assisted TCP/IPv4 checksums for the out-bound direction.
.It Cm tcp4csum-rx
Enable hardware-assisted TCP/IPv4 checksums for the in-bound direction.
.It Cm -tcp4csum-rx
Disable hardware-assisted TCP/IPv4 checksums for the in-bound direction.
.It Cm udp4csum-tx
Enable hardware-assisted UDP/IPv4 checksums for the out-bound direction.
.It Cm -udp4csum-tx
Disable hardware-assisted UDP/IPv4 checksums for the out-bound direction.
.It Cm udp4csum-rx
Enable hardware-assisted UDP/IPv4 checksums for the in-bound direction.
.It Cm -udp4csum-rx
Disable hardware-assisted UDP/IPv4 checksums for the in-bound direction.
.It Cm tcp6csum-tx
Enable hardware-assisted TCP/IPv6 checksums for the out-bound direction.
.It Cm -tcp6csum-tx
Disable hardware-assisted TCP/IPv6 checksums for the out-bound direction.
.It Cm tcp6csum-rx
Enable hardware-assisted TCP/IPv6 checksums for the in-bound direction.
.It Cm -tcp6csum-rx
Disable hardware-assisted TCP/IPv6 checksums for the in-bound direction.
.It Cm udp6csum-tx
Enable hardware-assisted UDP/IPv6 checksums for the out-bound direction.
.It Cm -udp6csum-tx
Disable hardware-assisted UDP/IPv6 checksums for the out-bound direction.
.It Cm udp6csum-rx
Enable hardware-assisted UDP/IPv6 checksums for the in-bound direction.
.It Cm -udp6csum-rx
Disable hardware-assisted UDP/IPv6 checksums for the in-bound direction.
.It Cm tso4
Enable hardware-assisted TCP/IPv4 segmentation on interfaces that
support it.
.It Cm -tso4
Disable hardware-assisted TCP/IPv4 segmentation on interfaces that
support it.
.It Cm tso6
Enable hardware-assisted TCP/IPv6 segmentation on interfaces that
support it.
.It Cm -tso6
Disable hardware-assisted TCP/IPv6 segmentation on interfaces that
support it.
.It Cm maxupd Ar n
If the driver is a
.Xr pfsync 4
pseudo-device, indicate the maximum number
of updates for a single state which can be collapsed into one.
This is an 8-bit number; the default value is 128.
.It Cm syncdev Ar iface
If the driver is a
.Xr pfsync 4
pseudo-device, use the specified interface
to send and receive pfsync state synchronisation messages.
.It Fl syncdev
If the driver is a
.Xr pfsync 4
pseudo-device, stop sending pfsync state
synchronisation messages over the network.
.It Cm syncpeer Ar peer_address
If the driver is a
.Xr pfsync 4
pseudo-device, make the pfsync link point-to-point rather than using
multicast to broadcast the state synchronisation messages.
The peer_address is the IP address of the other host taking part in
the pfsync cluster.
With this option,
.Xr pfsync 4
traffic can be protected using
.Xr ipsec 4 .
.It Fl syncpeer
If the driver is a
.Xr pfsync 4
pseudo-device, broadcast the packets using multicast.
.El
.Pp
.Nm
displays the current configuration for a network interface
when no optional parameters are supplied.
If a protocol family is specified,
.Nm
will report only the details specific to that protocol
family.
.Pp
If the
.Fl s
flag is passed before an interface name,
.Nm
will attempt to query the interface for its media status.
If the
interface supports reporting media status, and it reports that it does
not appear to be connected to a network,
.Nm
will exit with status of 1
.Pq false ;
otherwise, it will exit with a
zero
.Pq true
exit status.
Not all interface drivers support media
status reporting.
.Pp
If the
.Fl m
flag is passed before an interface name,
.Nm
will display all of the supported media for the specified interface.
If the
.Fl L
flag is supplied, address lifetime is displayed for IPv6 addresses,
as time offset string.
.Pp
Optionally, the
.Fl a
flag may be used instead of an interface name.
This flag instructs
.Nm
to display information about all interfaces in the system.
This is also the default behaviour when no arguments are given to
.Nm
on the command line.
When
.Fl a
is used, the output can be modified by adding more flags:
.Fl d
limits this to interfaces that are down,
.Fl u
limits this to interfaces that are up,
.Fl b
limits this to broadcast interfaces, and
.Fl s
omits interfaces which appear not to be connected to a network.
.Pp
The
.Fl 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
.Fl d
.Pq only list interfaces that are down ,
.Fl u
.Pq only list interfaces that are up ,
.Fl s
.Pq only list interfaces that may be connected ,
.Fl b
.Pq only list broadcast interfaces .
.Pp
The
.Fl C
flag may be used to list all of the interface cloners available on
the system, with no additional information.
Use of this flag is
mutually exclusive with all other flags and commands.
.Pp
The
.Fl v
flag prints statistics on packets sent and received on the given
interface.
If
.Fl h
is used in conjunction with
.Fl v ,
the byte statistics will be printed in "human-readable" format.
The
.Fl z
flag is identical to the
.Fl v
flag except that it zeros the interface input and output statistics
after printing them.
.Pp
The
.Fl w
flag may be used to wait
.Ar seconds
seconds for the
.Cm tentative
flag to be removed from all addresses.
0 seconds means to wait indefinitely until all addresses no longer have the
.Cm tentative
flag.
The optional
.Fl W
flag may be used to wait
.Ar seconds
seconds during the above time for the detached flag to be removed from all
addresses whose interface is marked ``up'' as well.
The detached flag is set when the interface does not have a carrier.
.Pp
The
.Fl N
flag is just the opposite of the
.Fl n
flag in
.Xr netstat 1
or in
.Xr route 8 :
it tells
.Nm
to try to resolve numbers to hostnames or to service names.
The default
.Nm
behavior is to print numbers instead of names.
.Pp
Only the super-user may modify the configuration of a network interface.
.Sh EXAMPLES
Add a link-layer (MAC) address to an Ethernet:
.Pp
.Ic ifconfig sip0 link 00:11:22:33:44:55
.Pp
Add and activate a link-layer (MAC) address:
.Pp
.Ic ifconfig sip0 link 00:11:22:33:44:55 active
.Sh 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.
.Sh SEE ALSO
.Xr netstat 1 ,
.Xr agr 4 ,
.Xr carp 4 ,
.Xr ifmedia 4 ,
.Xr netintro 4 ,
.Xr pfsync 4 ,
.Xr vlan 4 ,
.Xr ifconfig.if 5 ,
.\" .Xr eon 5 ,
.Xr rc 8 ,
.Xr routed 8
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.2 .