.\" Copyright (c) 1983, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     From: @(#)ifconfig.8	8.3 (Berkeley) 1/5/94
.\" $FreeBSD: src/sbin/ifconfig/ifconfig.8,v 1.142.2.6.2.1 2008/11/25 02:59:29 kensmith Exp $
.\"
.Dd June 20, 2008
.Dt IFCONFIG 8
.Os
.Sh NAME
.Nm ifconfig
.Nd configure network interface parameters
.Sh SYNOPSIS
.Nm
.Op Fl L
.Op Fl m
.Op Fl r
.Ar interface
.Op Cm create
.Op Ar address_family
.Oo
.Ar address
.Op Ar dest_address
.Oc
.Op Ar parameters
.Nm
.Ar interface
.Cm destroy
.Nm
.Fl a
.Op Fl L
.Op Fl d
.Op Fl m
.Op Fl r
.Op Fl u
.Op Fl v
.Op Ar address_family
.Nm
.Fl l
.Op Fl d
.Op Fl u
.Op Ar address_family
.Nm
.Op Fl L
.Op Fl d
.Op Fl m
.Op Fl r
.Op Fl u
.Op Fl v
.Op Fl C
.Nm
.Ar interface
.Cm vlan
.Ar vlan-tag
.Cm vlandev
.Ar iface
.Nm
.Ar interface
.Cm -vlandev
.Ar iface
.Nm
.Ar interface
.Cm bonddev
.Ar iface
.Nm
.Ar interface
.Cm -bonddev
.Ar iface
.Nm
.Ar interface
.Cm bondmode
.Ar lacp | static
.Sh DESCRIPTION
The
.Nm
utility is used to assign an address
to a network interface and/or configure
network interface parameters.
.Pp
The following options are available:
.Bl -tag -width indent
.It Ar address
For the
.Tn DARPA Ns -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 .
.Pp
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
.Li 192.168.0.1/16 .
.Pp
For the
.Dq inet6
family, it is also possible to specify the prefix length using the slash
notation, like
.Li ::1/128 .
See the
.Cm prefixlen
parameter below for more information.
.\" 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 IEEE 802 protocol
.\" (Ethernet, FDDI, and Token Ring) 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.
.Pp
The link-level
.Pq Dq link
address
is specified as a series of colon-separated hex digits.
This can be used to
e.g.\& set a new MAC address on an ethernet interface, though the
mechanism used is not ethernet-specific.
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 hardware is properly reprogrammed.
.It Ar address_family
Specify the
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 ipx ,
.\" .Dq iso ,
and
.Dq link .
.\" and
.\" .Dq ns .
The default is
.Dq inet .
.Dq ether
and
.Dq lladdr
are synonyms for
.Dq link .
.It Ar dest_address
Specify the address of the correspondent on the other end
of a point to point link.
.It Ar interface
This
parameter is a string of the form
.Dq name unit ,
for example,
.Dq Li en0 .
\.El
.Pp
The following parameters may be set with
.Nm :
.Bl -tag -width indent
.It Cm add
Another name for the
.Cm alias
parameter.
Introduced for compatibility
with
.Bsx .
.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.
If the address is on the same subnet as the first network address
for this interface, a non-conflicting netmask must be given.
Usually
.Li 0xffffffff
is most appropriate.
.It Fl 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.
.It Cm 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.
.It Cm arp
Enable the use of the Address Resolution Protocol
.Pq Xr arp 4
in mapping
between network level addresses and link level addresses (default).
This is currently implemented for mapping between
.Tn DARPA
Internet
addresses and
.Tn IEEE
802 48-bit MAC addresses (Ethernet, FDDI, and Token Ring addresses).
.It Fl arp
Disable the use of the Address Resolution Protocol
.Pq Xr arp 4 .
.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
Another name for the
.Fl alias
parameter.
.It Cm down
Mark an interface
.Dq down .
When an interface is marked
.Dq down ,
the system will not attempt to
transmit messages through that interface.
If possible, the interface will be reset to disable reception as well.
.It Cm ether
Another name for the
.Cm lladdr
parameter.
.\" .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 lladdr Ar 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
.Ar 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 hardware is properly reprogrammed.
.It Cm media Ar type
If the driver supports the media selection system, 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 10Mbit/s Ethernet
interface might support the use of either
.Tn AUI
or twisted pair connectors.
Setting the media type to
.Cm 10base5/AUI
would change the currently active connector to the AUI port.
Setting it to
.Cm 10baseT/UTP
would activate twisted pair.
Refer to the interfaces' driver
specific documentation or man page for a complete list of the
available types.
.It Cm mediaopt Ar opts
If the driver supports the media selection system, set the specified
media options on the interface.
The
.Ar 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.
.It Fl mediaopt Ar opts
If the driver supports the media selection system, disable the
specified media options on the interface.
.It Cm rxcsum , txcsum
If the driver supports user-configurable checksum offloading,
enable receive (or transmit) checksum offloading on the interface.
Some drivers may not be able to enable these flags independently
of each other, so setting one may also set the other.
The driver will offload as much checksum work as it can reliably
support, the exact level of offloading varies between drivers.
.It Fl rxcsum , txcsum
If the driver supports user-configurable checksum offloading,
disable receive (or transmit) checksum offloading on the interface.
These settings may not always be independent of each other.
.It Cm tso
If the driver supports
.Xr tcp 4
segmentation offloading, enable TSO on the interface.
Some drivers may not be able to support TSO for
.Xr ip 4
and
.Xr ip6 4
packets, so they may enable only one of them.
.It Fl tso
If the driver supports
.Xr tcp 4
segmentation offloading, disable TSO on the interface.
It will always disable TSO for
.Xr ip 4
and
.Xr ip6 4 .
.It Cm lro
If the driver supports
.Xr tcp 4
large receive offloading, enable LRO on the interface.
.It Fl lro
If the driver supports
.Xr tcp 4
large receive offloading, disable LRO on the interface.
.It Cm av
If supported by the driver, enable 802.1 AVB on the interface.
.It Fl av
If supported by the driver, disable 802.1 AVB on the interface.
.It Cm vlanmtu , vlanhwtag
If the driver offers user-configurable VLAN support, enable
reception of extended frames or tag processing in hardware,
respectively.
Note that this must be issued on a physical interface associated with
.Xr vlan 4 ,
not on a
.Xr vlan 4
interface itself.
.It Fl vlanmtu , vlanhwtag
If the driver offers user-configurable VLAN support, disable
reception of extended frames or tag processing in hardware,
respectively.
.It Cm 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 successful, the new device name is
printed to standard output unless the interface is renamed or destroyed
in the same
.Nm
invocation.
.It Cm destroy
Destroy the specified network pseudo-device.
.It Cm plumb
Another name for the
.Cm create
parameter.
Included for
.Tn Solaris
compatibility.
.It Cm unplumb
Another name for the
.Cm destroy
parameter.
Included for
.Tn Solaris
compatibility.
.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 additional hops
to the destination network or host.
.It Cm mtu Ar n
Set the maximum transmission unit of the interface to
.Ar 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 restrictions.
.It Cm netmask Ar mask
.\" (Inet and ISO.)
(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
.Ql 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
The netmask can also be specified in CIDR notation after the address.
See the
.Ar address
option above for more information.
.It Cm prefixlen Ar len
(Inet6 only.)
Specify that
.Ar len
bits are reserved for subdividing networks into sub-networks.
The
.Ar 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 parameter is omitted, 64 is used.
.Pp
The prefix can also be specified using the slash notation after the address.
See the
.Ar address
option above for more information.
.\" 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 from 1 may be useful
.\" for
.\" .Tn AFI
.\" 37 type addresses.
.It Cm remove
Another name for the
.Fl alias
parameter.
Introduced for compatibility
with
.Bsx .
.Sm off
.It Cm link Op Cm 0 No - Cm 2
.Sm on
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.
.Sm off
.It Fl link Op Cm 0 No - Cm 2
.Sm on
Disable special processing at the link level with the specified interface.
.It Cm up
Mark an interface
.Dq up .
This may be used to enable an interface after an
.Dq Nm Cm 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
The following parameters are specific to link aggregate interfaces:
.Bl -tag -width indent
.It Cm bonddev Ar iface
If the interface is a bond pseudo device, associate physical interface
.Ar iface
with it.  By default, the bond pseudo device is in LACP
(Link Aggregation Control Protocol) mode (see \fBbondmode\fR below).  In
this mode, the device conforms to the IEEE 802.3ad Link Aggregation 
specification.
.Pp
If this is the first physical interface to be associated with the bond
interface, the bond interface inherits the ethernet address from the
physical interface.  Physical interfaces that are added to the bond have
their ethernet address re-programmed so that all members of the bond have
the same ethernet address.  If the physical interface is subsequently
removed from the bond using
.Fl bonddev ,
a new ethernet address is chosen from the remaining interfaces, and all
interfaces are re-programmed again with the new ethernet address.  If no
remaining interfaces exist, the bond interface's ethernet address is cleared.
.Pp
If the specified physical interface
.Ar iface
is not capable of having its ethernet address re-programmed, the
.Cm bonddev
command will fail.
.Pp
Once the physical interface
.Ar iface
is successfully associated with the bond interface, all received packets
are diverted to the bond interface.  The physical interface is no longer
useable on its own, and remains that way until it is removed from the bond using
.Fl bonddev .
.Pp
It is possible that the specified interface
.Ar iface
is not capable of aggregating, and may remain unused until the operating
conditions change.
.Pp
The link status of the bond interface depends on the state of link aggregation.
If no active partner is detected, the link status will remain inactive.
.Pp
To monitor the 802.3ad Link Aggregation state, use the
.Fl b
option.
.Pp
A physical interface that is associated with a vlan pseudo device cannot
at the same time be associated with a bond pseudo device.  A physical interface
cannot be associated with more than one bond pseudo device at the same time.
.Pp
It is not possible to associate a bond with pseudo interfaces such as vlan.
Only physical ethernet interfaces may be associated with a bond.
.It Fl bonddev Ar iface
If the interface is a bond pseudo device, disassociate the physical interface
.Ar iface
from it.  Before the interface is removed from the bond, the bond device
announces to the link partner that the interface is now individual and
no longer aggregatable.
If the physical
.Ar iface
is the last interface in the bond, the bond interface clears its link address.
.It Cm bondmode Ar lacp | static
If the interface is a bond pseudo device, this option will set the \fImode\fR
on the bond interface.  The two currently supported modes are
.Ar lacp
and 
.Ar static .
The default mode is
.Ar lacp .
.Pp
To enable static mode (and turn off LACP), specify
.Ar static .
In static mode, a member interface is made an active part of the 
link aggregate as long as the link status is active.
.Pp
To re-enable LACP mode, specify
.Ar lacp .
.El
.Pp
The following parameters are specific to IP tunnel interfaces,
.Xr gif 4 :
.Bl -tag -width indent
.It Cm tunnel Ar src_addr dest_addr
Configure the physical source and destination address for IP tunnel
interfaces.
The arguments
.Ar src_addr
and
.Ar dest_addr
are interpreted as the outer source/destination for the encapsulating
IPv4/IPv6 header.
.It Fl tunnel
Unconfigure the physical source and destination address for IP tunnel
interfaces previously configured with
.Cm tunnel .
.It Cm deletetunnel
Another name for the
.Fl tunnel
parameter.
.El
.Pp
The following parameters are specific to bridge interfaces:
.Bl -tag -width indent
.It Cm addm Ar interface
Add the interface named by
.Ar interface
as a member of the bridge.
The interface is put into promiscuous mode
so that it can receive every packet sent on the network.
.It Cm deletem Ar interface
Remove the interface named by
.Ar interface
from the bridge.
Promiscuous mode is disabled on the interface when
it is removed from the bridge.
.It Cm maxaddr Ar size
Set the size of the bridge address cache to
.Ar size .
The default is 100 entries.
.It Cm timeout Ar seconds
Set the timeout of address cache entries to
.Ar seconds
seconds.
If
.Ar seconds
is zero, then address cache entries will not be expired.
The default is 240 seconds.
.It Cm addr
Display the addresses that have been learned by the bridge.
.It Cm static Ar interface-name Ar address
Add a static entry into the address cache pointing to
.Ar interface-name .
Static entries are never aged out of the cache or re-placed, even if the
address is seen on a different interface.
.It Cm deladdr Ar address
Delete
.Ar address
from the address cache.
.It Cm flush
Delete all dynamically-learned addresses from the address cache.
.It Cm flushall
Delete all addresses, including static addresses, from the address cache.
.It Cm discover Ar interface
Mark an interface as a
.Dq discovering
interface.
When the bridge has no address cache entry
(either dynamic or static)
for the destination address of a packet,
the bridge will forward the packet to all
member interfaces marked as
.Dq discovering .
This is the default for all interfaces added to a bridge.
.It Cm -discover Ar interface
Clear the
.Dq discovering
attribute on a member interface.
For packets without the
.Dq discovering
attribute, the only packets forwarded on the interface are broadcast
or multicast packets and packets for which the destination address
is known to be on the interface's segment.
.It Cm learn Ar interface
Mark an interface as a
.Dq learning
interface.
When a packet arrives on such an interface, the source
address of the packet is entered into the address cache as being a
destination address on the interface's segment.
This is the default for all interfaces added to a bridge.
.It Cm -learn Ar interface
Clear the
.Dq learning
attribute on a member interface.
.It Cm sticky Ar interface
Mark an interface as a
.Dq sticky
interface.
Dynamically learned address entries are treated at static once entered into
the cache.
Sticky entries are never aged out of the cache or replaced, even if the
address is seen on a different interface.
.It Cm -sticky Ar interface
Clear the
.Dq sticky
attribute on a member interface.
.It Cm private Ar interface
Mark an interface as a
.Dq private
interface.
A private interface does not forward any traffic to any other port that is also
a private interface.
.It Cm -private Ar interface
Clear the
.Dq private
attribute on a member interface.
.It Cm span Ar interface
Add the interface named by
.Ar interface
as a span port on the bridge.
Span ports transmit a copy of every frame received by the bridge.
This is most useful for snooping a bridged network passively on
another host connected to one of the span ports of the bridge.
.It Cm -span Ar interface
Delete the interface named by
.Ar interface
from the list of span ports of the bridge.
.It Cm stp Ar interface
Enable Spanning Tree protocol on
.Ar interface .
The
.Xr if_bridge 4
driver has support for the IEEE 802.1D Spanning Tree protocol (STP).
Spanning Tree is used to detect and remove loops in a network topology.
.It Cm -stp Ar interface
Disable Spanning Tree protocol on
.Ar interface .
This is the default for all interfaces added to a bridge.
.It Cm edge Ar interface
Set
.Ar interface
as an edge port.
An edge port connects directly to end stations cannot create bridging
loops in the network, this allows it to transition straight to forwarding.
.It Cm -edge Ar interface
Disable edge status on
.Ar interface .
.It Cm autoedge Ar interface
Allow
.Ar interface
to automatically detect edge status.
This is the default for all interfaces added to a bridge.
.It Cm -autoedge Ar interface
Disable automatic edge status on
.Ar interface .
.It Cm ptp Ar interface
Set the
.Ar interface
as a point to point link.
This is required for straight transitions to forwarding and
should be enabled on a direct link to another RSTP capable switch.
.It Cm -ptp Ar interface
Disable point to point link status on
.Ar interface .
This should be disabled for a half duplex link and for an interface
connected to a shared network segment,
like a hub or a wireless network.
.It Cm autoptp Ar interface
Automatically detect the point to point status on
.Ar interface
by checking the full duplex link status.
This is the default for interfaces added to the bridge.
.It Cm -autoptp Ar interface
Disable automatic point to point link detection on
.Ar interface .
.It Cm maxage Ar seconds
Set the time that a Spanning Tree protocol configuration is valid.
The default is 20 seconds.
The minimum is 6 seconds and the maximum is 40 seconds.
.It Cm fwddelay Ar seconds
Set the time that must pass before an interface begins forwarding
packets when Spanning Tree is enabled.
The default is 15 seconds.
The minimum is 4 seconds and the maximum is 30 seconds.
.It Cm hellotime Ar seconds
Set the time between broadcasting of Spanning Tree protocol
configuration messages.
The hello time may only be changed when operating in legacy stp mode.
The default is 2 seconds.
The minimum is 1 second and the maximum is 2 seconds.
.It Cm priority Ar value
Set the bridge priority for Spanning Tree.
The default is 32768.
The minimum is 0 and the maximum is 61440.
.It Cm proto Ar value
Set the Spanning Tree protocol.
The default is rstp.
The available options are stp and rstp.
.It Cm holdcnt Ar value
Set the transmit hold count for Spanning Tree.
This is the number of packets transmitted before being rate limited.
The default is 6.
The minimum is 1 and the maximum is 10.
.It Cm ifpriority Ar interface Ar value
Set the Spanning Tree priority of
.Ar interface
to
.Ar value .
The default is 128.
The minimum is 0 and the maximum is 240.
.It Cm ifpathcost Ar interface Ar value
Set the Spanning Tree path cost of
.Ar interface
to
.Ar value .
The default is calculated from the link speed.
To change a previously selected path cost back to automatic, set the
cost to 0.
The minimum is 1 and the maximum is 200000000.
.It Cm ifmaxaddr Ar interface Ar size
Set the maximum number of hosts allowed from an interface, packets with unknown
source addresses are dropped until an existing host cache entry expires or is
removed.
Set to 0 to disable.
.El
.Pp
The following parameters are specific to vlan interfaces:
.Bl -tag -width indent
.It Cm vlan Ar vlan_tag
Set the VLAN tag value to
.Ar vlan_tag .
This value is a 16-bit number which is used to create an 802.1Q
VLAN header for packets sent from the
.Xr vlan 4
interface.
Note that
.Cm vlan
and
.Cm vlandev
must both be set at the same time.
.It Cm vlandev Ar iface
Associate the physical interface
.Ar iface
with a
.Xr vlan 4
interface.
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 parent interface with the correct VLAN tag will be diverted to
the associated
.Xr vlan 4
pseudo-interface.
The
.Xr vlan 4
interface is assigned a
copy of the parent interface's flags and the parent's ethernet address.
The
.Cm vlandev
and
.Cm vlan
must both be set at the same time.
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.
.Pp
Note: if the hardware tagging capability
is set on the parent interface, the
.Xr vlan 4
pseudo
interface's behavior changes:
the
.Xr vlan 4
interface recognizes that the
parent interface supports insertion and extraction of VLAN tags on its
own (usually in firmware) and that it should pass packets to and from
the parent unaltered.
.It Fl vlandev Op Ar iface
If the driver is a
.Xr vlan 4
pseudo device, disassociate the parent interface from it.
This breaks the link between the
.Xr vlan 4
interface and its parent,
clears its VLAN tag, flags and its link address and shuts the interface down.
The
.Ar iface
argument is useless and hence deprecated.
.El
.Pp
The
.Nm
utility 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 m
flag is passed before an interface name,
.Nm
will display the capability list and all
of the supported media for the specified interface.
.Pp
If
.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.
The
.Fl d
flag limits this to interfaces that are down, and
.Fl u
limits this to interfaces that are up.
When no arguments are given,
.Fl a
is implied.
.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
(only list interfaces that are down)
and
.Fl u
(only list interfaces that are up).
.Pp
The
.Fl v
flag may be used to get more verbose status for an interface.
.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 r
flag may be used to show additional information related to the count of route references on the network interface.
.Pp
For bridge interfaces, the list of addresses learned by the bridge is not shown when displaying information about 
all interfaces except when the 
.Fl v
flag is used.
.Pp
Only the super-user may modify the configuration of a network interface.
.Sh NOTES
The media selection system is relatively new and only some drivers support
it (or have need for it).
.Sh EXAMPLES
Assign the IPv4 address
.Li 192.0.2.10 ,
with a network mask of
.Li 255.255.255.0 ,
to the interface
.Li en0 :
.Dl # ifconfig en0 inet 192.0.2.10 netmask 255.255.255.0
.Pp
Add the IPv4 address
.Li 192.0.2.45 ,
with the CIDR network prefix
.Li /28 ,
to the interface
.Li en0 ,
using
.Cm add
as a synonym for the canonical form of the option
.Cm alias :
.Dl # ifconfig en0 inet 192.0.2.45/28 add
.Pp
Remove the IPv4 address
.Li 192.0.2.45
from the interface
.Li en0 :
.Dl # ifconfig en0 inet 192.0.2.45 -alias
.Pp
Add the IPv6 address
.Li 2001:DB8:DBDB::123/48
to the interface
.Li en0 :
.Dl # ifconfig en0 inet6 2001:db8:bdbd::123 prefixlen 48 alias
Note that lower case hexadecimal IPv6 addresses are acceptable.
.Pp
Remove the IPv6 address added in the above example,
using the
.Li /
character as shorthand for the network prefix,
and using
.Cm delete
as a synonym for the canonical form of the option
.Fl alias :
.Dl # ifconfig en0 inet6 2001:db8:bdbd::123/48 delete
.Pp
Configure the interface
.Li en1 ,
to use 100baseTX, full duplex Ethernet media options:
.Dl # ifconfig en1 media 100baseTX mediaopt full-duplex
.Pp
Create the software network interface
.Li gif1 :
.Dl # ifconfig gif1 create
.Pp
Destroy the software network interface
.Li gif1 :
.Dl # ifconfig gif1 destroy
.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 netintro 4 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
utility appeared in
.Bx 4.2 .
.Sh BUGS
Basic IPv6 node operation requires a link-local address on each
interface configured for IPv6.
Normally, such an address is automatically configured by the
kernel on each interface added to the system; this behaviour may
be disabled by setting the sysctl MIB variable
.Va net.inet6.ip6.auto_linklocal
to 0.
.Pp
If you delete such an address using
.Nm ,
the kernel may act very odd.
Do this at your own risk.