xref: /freebsd/share/man/man9/ieee80211.9 (revision 62cfcf62f627e5093fb37026a6d8c98e4d2ef04c)

.\"
.\" Copyright (c) 2004 Bruce M. Simpson <bms@spc.org>
.\" Copyright (c) 2004 Darron Broad <darron@kewl.org>
.\" Copyright (c) 2009 Sam Leffler, Errno Consulting
.\" 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.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
.\"
.\" $FreeBSD$
.\"
.Dd December 31, 2017
.Dt IEEE80211 9
.Os
.Sh NAME
.Nm IEEE80211
.Nd 802.11 network layer
.Sh SYNOPSIS
.In net80211/ieee80211_var.h
.Ft void
.Fn ieee80211_ifattach "struct ieee80211com *ic"
.Ft void
.Fn ieee80211_ifdetach "struct ieee80211com *ic"
.Ft int
.Fn ieee80211_mhz2ieee "u_int freq" "u_int flags"
.Ft int
.Fn ieee80211_chan2ieee "struct ieee80211com *ic" "const struct ieee80211_channel *c"
.Ft u_int
.Fn ieee80211_ieee2mhz "u_int chan" "u_int flags"
.Ft int
.Fn ieee80211_media_change "struct ifnet *ifp"
.Ft void
.Fn ieee80211_media_status "struct ifnet *ifp" "struct ifmediareq *imr"
.Ft int
.Fn ieee80211_setmode "struct ieee80211com *ic" "enum ieee80211_phymode mode"
.Ft enum ieee80211_phymode
.Fo ieee80211_chan2mode
.Fa "const struct ieee80211_channel *chan"
.Fc
.Ft int
.Fo ieee80211_rate2media
.Fa "struct ieee80211com *ic" "int rate" "enum ieee80211_phymode mode"
.Fc
.Ft int
.Fn ieee80211_media2rate "int mword"
.Sh DESCRIPTION
IEEE 802.11 device drivers are written to use the infrastructure provided
by the
.Nm
software layer.
This software provides a support framework for drivers that includes
ifnet cloning, state management, and a user management API by which
applications interact with 802.11 devices.
Most drivers depend on the
.Nm
layer for protocol services but devices that off-load functionality
may bypass the layer to connect directly to the device
(e.g. the
.Xr ndis 4
emulation support does this).
.Pp
A
.Nm
device driver implements a virtual radio API that is exported to
users through network interfaces (aka vaps) that are cloned from the
underlying device.
These interfaces have an operating mode
(station, adhoc, hostap, wds, monitor, etc.\&)
that is fixed for the lifetime of the interface.
Devices that can support multiple concurrent interfaces allow
multiple vaps to be cloned.
This enables construction of interesting applications such as
an AP vap and one or more WDS vaps
or multiple AP vaps, each with a different security model.
The
.Nm
layer virtualizes most 802.11 state
and coordinates vap state changes including scheduling multiple vaps.
State that is not virtualized includes the current channel and
WME/WMM parameters.
Protocol processing is typically handled entirely in the
.Nm
layer with drivers responsible purely for moving data between the host
and device.
Similarly,
.Nm
handles most
.Xr ioctl 2
requests without entering the driver;
instead drivers are notified of state changes that
require their involvement.
.Pp
The virtual radio interface defined by the
.Nm
layer means that drivers must be structured to follow specific rules.
Drivers that support only a single interface at any time must still
follow these rules.
.Pp
Most of these functions require that attachment to the stack is performed
before calling.
.Pp
.\"
The
.Fn ieee80211_ifattach
function attaches the wireless network interface
.Fa ic
to the 802.11 network stack layer.
This function must be called before using any of the
.Nm
functions which need to store driver state across invocations.
.Pp
.\"
The
.Fn ieee80211_ifdetach
function frees any
.Nm
structures associated with the driver, and performs Ethernet and BPF
detachment on behalf of the caller.
.Pp
.\"
The
.Fn ieee80211_mhz2ieee
utility function converts the frequency
.Fa freq
(specified in MHz) to an IEEE 802.11 channel number.
The
.Fa flags
argument is a hint which specifies whether the frequency is in
the 2GHz ISM band
.Pq Vt IEEE80211_CHAN_2GHZ
or the 5GHz band
.Pq Vt IEEE80211_CHAN_5GHZ ;
appropriate clipping of the result is then performed.
.Pp
.\"
The
.Fn ieee80211_chan2ieee
function converts the channel specified in
.Fa *c
to an IEEE channel number for the driver
.Fa ic .
If the conversion would be invalid, an error message is printed to the
system console.
This function REQUIRES that the driver is hooked up to the
.Nm
subsystem.
.Pp
.\"
The
.Fn ieee80211_ieee2mhz
utility function converts the IEEE channel number
.Ft chan
to a frequency (in MHz).
The
.Fa flags
argument is a hint which specifies whether the frequency is in
the 2GHz ISM band
.Pq Vt IEEE80211_CHAN_2GHZ
or the 5GHz band
.Pq Vt IEEE80211_CHAN_5GHZ ;
appropriate clipping of the result is then performed.
.Pp
.\"
The
.Fn ieee80211_media_status
and
.Fn ieee80211_media_change
functions are device-independent handlers for
.Vt ifmedia
commands and are not intended to be called directly.
.Pp
.\"
The
.Fn ieee80211_setmode
function is called from within the 802.11 stack to change the mode
of the driver's PHY; it is not intended to be called directly.
.Pp
.\"
The
.Fn ieee80211_chan2mode
function returns the PHY mode required for use with the channel
.Fa chan .
This is typically used when selecting a rate set, to be advertised in
beacons, for example.
.Pp
.\"
The
.Fn ieee80211_rate2media
function converts the bit rate
.Fa rate
(measured in units of 0.5Mbps) to an
.Vt ifmedia
sub-type, for the device
.Fa ic
running in PHY mode
.Fa mode .
The
.Fn ieee80211_media2rate
performs the reverse of this conversion, returning the bit rate (in 0.5Mbps
units) corresponding to an
.Vt ifmedia
sub-type.
.
.Sh DATA STRUCTURES
The virtual radio architecture splits state between a single per-device
.Vt ieee80211com
structure and one or more
.Vt ieee80211vap
structures.
Drivers are expected to setup various shared state in these structures
at device attach and during vap creation but otherwise should treat them
as read-only.
The
.Vt ieee80211com
structure is allocated by the
.Nm
layer as adjunct data to a device's
.Vt ifnet ;
it is accessed through the
.Vt if_l2com
structure member.
The
.Vt ieee80211vap
structure is allocated by the driver in the
.Dq vap create
method
and should be extended with any driver-private state.
This technique of giving the driver control to allocate data structures
is used for other
.Nm
data structures and should be exploited to maintain driver-private state
together with public
.Nm
state.
.Pp
The other main data structures are the station, or node, table
that tracks peers in the local BSS, and the channel table that defines
the current set of available radio channels.
Both tables are bound to the
.Vt ieee80211com
structure and shared by all vaps.
Long-lasting references to a node are counted to guard against
premature reclamation.
In particular every packet sent/received holds a node reference
(either explicitly for transmit or implicitly on receive).
.Pp
The
.Vt ieee80211com
and
.Vt ieee80211vap
structures also hold a collection of method pointers that drivers
fill-in and/or override to take control of certain operations.
These methods are the primary way drivers are bound to the
.Nm
layer and are described below.
.Sh DRIVER ATTACH/DETACH
Drivers attach to the
.Nm
layer with the
.Fn ieee80211_ifattach
function.
The driver is expected to allocate and setup any device-private
data structures before passing control.
The
.Vt ieee80211com
structure must be pre-initialized with state required to setup the
.Nm
layer:
.Bl -tag -width ic_channels
.It Dv ic_ifp
Backpointer to the physical device's ifnet.
.It Dv ic_caps
Device/driver capabilities; see below for a complete description.
.It Dv ic_channels
Table of channels the device is capable of operating on.
This is initially provided by the driver but may be changed
through calls that change the regulatory state.
.It Dv ic_nchan
Number of entries in
.Dv ic_channels .
.El
.Pp
On return from
.Fn ieee80211_ifattach
the driver is expected to override default callback functions in the
.Vt ieee80211com
structure to register it's private routines.
Methods marked with a
.Dq *
must be provided by the driver.
.Bl -tag -width ic_channels
.It Dv ic_vap_create*
Create a vap instance of the specified type (operating mode).
Any fixed BSSID and/or MAC address is provided.
Drivers that support multi-bssid operation may honor the requested BSSID
or assign their own.
.It Dv ic_vap_delete*
Destroy a vap instance created with
.Dv ic_vap_create .
.It Dv ic_getradiocaps
Return the list of calibrated channels for the radio.
The default method returns the current list of channels
(space permitting).
.It Dv ic_setregdomain
Process a request to change regulatory state.
The routine may reject a request or constrain changes (e.g. reduce
transmit power caps).
The default method accepts all proposed changes.
.It Dv ic_send_mgmt
Send an 802.11 management frame.
The default method fabricates the frame using
.Nm
state and passes it to the driver through the
.Dv ic_raw_xmit
method.
.It Dv ic_raw_xmit
Transmit a raw 802.11 frame.
The default method drops the frame and generates a message on the console.
.It Dv ic_updateslot
Update hardware state after an 802.11 IFS slot time change.
There is no default method; the pointer may be NULL in which case
it will not be used.
.It Dv ic_update_mcast
Update hardware for a change in the multicast packet filter.
The default method prints a console message.
.It Dv ic_update_promisc
Update hardware for a change in the promiscuous mode setting.
The default method prints a console message.
.It Dv ic_newassoc
Update driver/device state for association to a new AP (in station mode)
or when a new station associates (e.g. in AP mode).
There is no default method; the pointer may be NULL in which case
it will not be used.
.It Dv ic_node_alloc
Allocate and initialize a
.Vt ieee80211_node
structure.
This method cannot sleep.
The default method allocates zero'd memory using
.Xr malloc 9 .
Drivers should override this method to allocate extended storage
for their own needs.
Memory allocated by the driver must be tagged with
.Dv M_80211_NODE
to balance the memory allocation statistics.
.It Dv ic_node_free
Reclaim storage of a node allocated by
.Dv ic_node_alloc  .
Drivers are expected to
.Em interpose
their own method to cleanup private state but must call through
this method to allow
.Nm
to reclaim it's private state.
.It Dv ic_node_cleanup
Cleanup state in a
.Vt ieee80211_node
created by
.Dv ic_node_alloc .
This operation is distinguished from
.Dv ic_node_free
in that it may be called long before the node is actually reclaimed
to cleanup adjunct state.
This can happen, for example, when a node must not be reclaimed
due to references held by packets in the transmit queue.
Drivers typically interpose
.Dv ic_node_cleanup
instead of
.Dv ic_node_free .
.It Dv ic_node_age
Age, and potentially reclaim, resources associated with a node.
The default method ages frames on the power-save queue (in AP mode)
and pending frames in the receive reorder queues (for stations using A-MPDU).
.It Dv ic_node_drain
Reclaim all optional resources associated with a node.
This call is used to free up resources when they are in short supply.
.It Dv ic_node_getrssi
Return the Receive Signal Strength Indication (RSSI) in .5 dBm units for
the specified node.
This interface returns a subset of the information
returned by
.Dv ic_node_getsignal .
The default method calculates a filtered average over the last ten
samples passed in to
.Xr ieee80211_input 9
or
.Xr ieee80211_input_all 9 .
.It Dv ic_node_getsignal
Return the RSSI and noise floor (in .5 dBm units) for a station.
The default method calculates RSSI as described above;
the noise floor returned is the last value supplied to
.Xr ieee80211_input 9
or
.Xr ieee80211_input_all 9 .
.It Dv ic_node_getmimoinfo
Return MIMO radio state for a station in support of the
.Dv IEEE80211_IOC_STA_INFO
ioctl request.
The default method returns nothing.
.It Dv ic_scan_start*
Prepare driver/hardware state for scanning.
This callback is done in a sleepable context.
.It Dv ic_scan_end*
Restore driver/hardware state after scanning completes.
This callback is done in a sleepable context.
.It Dv ic_set_channel*
Set the current radio channel using
.Vt ic_curchan .
This callback is done in a sleepable context.
.It Dv ic_scan_curchan
Start scanning on a channel.
This method is called immediately after each channel change
and must initiate the work to scan a channel and schedule a timer
to advance to the next channel in the scan list.
This callback is done in a sleepable context.
The default method handles active scan work (e.g. sending ProbeRequest
frames), and schedules a call to
.Xr ieee80211_scan_next 9
according to the maximum dwell time for the channel.
Drivers that off-load scan work to firmware typically use this method
to trigger per-channel scan activity.
.It Dv ic_scan_mindwell
Handle reaching the minimum dwell time on a channel when scanning.
This event is triggered when one or more stations have been found on
a channel and the minimum dwell time has been reached.
This callback is done in a sleepable context.
The default method signals the scan machinery to advance
to the next channel as soon as possible.
Drivers can use this method to preempt further work (e.g. if scanning
is handled by firmware) or ignore the request to force maximum dwell time
on a channel.
.It Dv ic_recv_action
Process a received Action frame.
The default method points to
.Xr ieee80211_recv_action 9
which provides a mechanism for setting up handlers for each Action frame class.
.It Dv ic_send_action
Transmit an Action frame.
The default method points to
.Xr ieee80211_send_action 9
which provides a mechanism for setting up handlers for each Action frame class.
.It Dv ic_ampdu_enable
Check if transmit A-MPDU should be enabled for the specified station and AC.
The default method checks a per-AC traffic rate against a per-vap
threshold to decide if A-MPDU should be enabled.
This method also rate-limits ADDBA requests so that requests are not
made too frequently when a receiver has limited resources.
.It Dv ic_addba_request
Request A-MPDU transmit aggregation.
The default method sets up local state and issues an
ADDBA Request Action frame.
Drivers may interpose this method if they need to setup private state
for handling transmit A-MPDU.
.It Dv ic_addb_response
Process a received ADDBA Response Action frame and setup resources as
needed for doing transmit A-MPDU.
.It Dv ic_addb_stop
Shutdown an A-MPDU transmit stream for the specified station and AC.
The default method reclaims local state after sending a DelBA Action frame.
.It Dv ic_bar_response
Process a response to a transmitted BAR control frame.
.It Dv ic_ampdu_rx_start
Prepare to receive A-MPDU data from the specified station for the TID.
.It Dv ic_ampdu_rx_stop
Terminate receipt of A-MPDU data from the specified station for the TID.
.El
.Pp
Once the
.Nm
layer is attached to a driver there are two more steps typically done
to complete the work:
.Bl -enum
.It
Setup
.Dq radiotap support
for capturing raw 802.11 packets that pass through the device.
This is done with a call to
.Xr ieee80211_radiotap_attach 9 .
.It
Do any final device setup like enabling interrupts.
.El
.Pp
State is torn down and reclaimed with a call to
.Fn ieee80211_ifdetach .
Note this call may result in multiple callbacks into the driver
so it should be done before any critical driver state is reclaimed.
On return from
.Fn ieee80211_ifdetach
all associated vaps and ifnet structures are reclaimed or inaccessible
to user applications so it is safe to teardown driver state without
worry about being re-entered.
The driver is responsible for calling
.Xr if_free 9
on the ifnet it allocated for the physical device.
.Sh DRIVER CAPABILITIES
Driver/device capabilities are specified using several sets of flags
in the
.Vt ieee80211com
structure.
General capabilities are specified by
.Vt ic_caps .
Hardware cryptographic capabilities are specified by
.Vt ic_cryptocaps .
802.11n capabilities, if any, are specified by
.Vt ic_htcaps .
The
.Nm
layer propagates a subset of these capabilities to each vap through
the equivalent fields:
.Vt iv_caps ,
.Vt iv_cryptocaps ,
and
.Vt iv_htcaps .
The following general capabilities are defined:
.Bl -tag -width IEEE80211_C_8023ENCAP
.It Dv IEEE80211_C_STA
Device is capable of operating in station (aka Infrastructure) mode.
.It Dv IEEE80211_C_8023ENCAP
Device requires 802.3-encapsulated frames be passed for transmit.
By default
.Nm
will encapsulate all outbound frames as 802.11 frames (without a PLCP header).
.It Dv IEEE80211_C_FF
Device supports Atheros Fast-Frames.
.It Dv IEEE80211_C_TURBOP
Device supports Atheros Dynamic Turbo mode.
.It Dv IEEE80211_C_IBSS
Device is capable of operating in adhoc/IBSS mode.
.It Dv IEEE80211_C_PMGT
Device supports dynamic power-management (aka power save) in station mode.
.It Dv IEEE80211_C_HOSTAP
Device is capable of operating as an Access Point in Infrastructure mode.
.It Dv IEEE80211_C_AHDEMO
Device is capable of operating in Adhoc Demo mode.
In this mode the device is used purely to send/receive raw 802.11 frames.
.It Dv IEEE80211_C_SWRETRY
Device supports software retry of transmitted frames.
.It Dv IEEE80211_C_TXPMGT
Device support dynamic transmit power changes on transmitted frames;
also known as Transmit Power Control (TPC).
.It Dv IEEE80211_C_SHSLOT
Device supports short slot time operation (for 802.11g).
.It Dv IEEE80211_C_SHPREAMBLE
Device supports short preamble operation (for 802.11g).
.It Dv IEEE80211_C_MONITOR
Device is capable of operating in monitor mode.
.It Dv IEEE80211_C_DFS
Device supports radar detection and/or DFS.
DFS protocol support can be handled by
.Nm
but the device must be capable of detecting radar events.
.It Dv IEEE80211_C_MBSS
Device is capable of operating in MeshBSS (MBSS) mode
(as defined by 802.11s Draft 3.0).
.It Dv IEEE80211_C_WPA1
Device supports WPA1 operation.
.It Dv IEEE80211_C_WPA2
Device supports WPA2/802.11i operation.
.It Dv IEEE80211_C_BURST
Device supports frame bursting.
.It Dv IEEE80211_C_WME
Device supports WME/WMM operation
(at the moment this is mostly support for sending and receiving
QoS frames with EDCF).
.It Dv IEEE80211_C_WDS
Device supports transmit/receive of 4-address frames.
.It Dv IEEE80211_C_BGSCAN
Device supports background scanning.
.It Dv IEEE80211_C_TXFRAG
Device supports transmit of fragmented 802.11 frames.
.It Dv IEEE80211_C_TDMA
Device is capable of operating in TDMA mode.
.El
.Pp
The follow general crypto capabilities are defined.
In general
.Nm
will fall-back to software support when a device is not capable
of hardware acceleration of a cipher.
This can be done on a per-key basis.
.Nm
can also handle software
.Dv Michael
calculation combined with hardware
.Dv AES
acceleration.
.Bl -tag -width IEEE80211_C_8023ENCAP
.It Dv IEEE80211_CRYPTO_WEP
Device supports hardware WEP cipher.
.It Dv IEEE80211_CRYPTO_TKIP
Device supports hardware TKIP cipher.
.It Dv IEEE80211_CRYPTO_AES_OCB
Device supports hardware AES-OCB cipher.
.It Dv IEEE80211_CRYPTO_AES_CCM
Device supports hardware AES-CCM cipher.
.It Dv IEEE80211_CRYPTO_TKIPMIC
Device supports hardware Michael for use with TKIP.
.It Dv IEEE80211_CRYPTO_CKIP
Devices supports hardware CKIP cipher.
.El
.Pp
The follow general 802.11n capabilities are defined.
The first capabilities are defined exactly as they appear in the
802.11n specification.
Capabilities beginning with IEEE80211_HTC_AMPDU are used solely by the
.Nm
layer.
.Bl -tag -width IEEE80211_C_8023ENCAP
.It Dv IEEE80211_HTCAP_CHWIDTH40
Device supports 20/40 channel width operation.
.It Dv IEEE80211_HTCAP_SMPS_DYNAMIC
Device supports dynamic SM power save operation.
.It Dv IEEE80211_HTCAP_SMPS_ENA
Device supports static SM power save operation.
.It Dv IEEE80211_HTCAP_GREENFIELD
Device supports Greenfield preamble.
.It Dv IEEE80211_HTCAP_SHORTGI20
Device supports Short Guard Interval on 20MHz channels.
.It Dv IEEE80211_HTCAP_SHORTGI40
Device supports Short Guard Interval on 40MHz channels.
.It Dv IEEE80211_HTCAP_TXSTBC
Device supports Space Time Block Convolution (STBC) for transmit.
.It Dv IEEE80211_HTCAP_RXSTBC_1STREAM
Device supports 1 spatial stream for STBC receive.
.It Dv IEEE80211_HTCAP_RXSTBC_2STREAM
Device supports 1-2 spatial streams for STBC receive.
.It Dv IEEE80211_HTCAP_RXSTBC_3STREAM
Device supports 1-3 spatial streams for STBC receive.
.It Dv IEEE80211_HTCAP_MAXAMSDU_7935
Device supports A-MSDU frames up to 7935 octets.
.It Dv IEEE80211_HTCAP_MAXAMSDU_3839
Device supports A-MSDU frames up to 3839 octets.
.It Dv IEEE80211_HTCAP_DSSSCCK40
Device supports use of DSSS/CCK on 40MHz channels.
.It Dv IEEE80211_HTCAP_PSMP
Device supports PSMP.
.It Dv IEEE80211_HTCAP_40INTOLERANT
Device is intolerant of 40MHz wide channel use.
.It Dv IEEE80211_HTCAP_LSIGTXOPPROT
Device supports L-SIG TXOP protection.
.It Dv IEEE80211_HTC_AMPDU
Device supports A-MPDU aggregation.
Note that any 802.11n compliant device must support A-MPDU receive
so this implicitly means support for
.Em transmit
of A-MPDU frames.
.It Dv IEEE80211_HTC_AMSDU
Device supports A-MSDU aggregation.
Note that any 802.11n compliant device must support A-MSDU receive
so this implicitly means support for
.Em transmit
of A-MSDU frames.
.It Dv IEEE80211_HTC_HT
Device supports High Throughput (HT) operation.
This capability must be set to enable 802.11n functionality
in
.Nm .
.It Dv IEEE80211_HTC_SMPS
Device supports MIMO Power Save operation.
.It Dv IEEE80211_HTC_RIFS
Device supports Reduced Inter Frame Spacing (RIFS).
.El
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr ndis 4 ,
.Xr ieee80211_amrr 9 ,
.Xr ieee80211_beacon 9 ,
.Xr ieee80211_bmiss 9 ,
.Xr ieee80211_crypto 9 ,
.Xr ieee80211_ddb 9 ,
.Xr ieee80211_input 9 ,
.Xr ieee80211_node 9 ,
.Xr ieee80211_output 9 ,
.Xr ieee80211_proto 9 ,
.Xr ieee80211_radiotap 9 ,
.Xr ieee80211_regdomain 9 ,
.Xr ieee80211_scan 9 ,
.Xr ieee80211_vap 9 ,
.Xr ifnet 9 ,
.Xr malloc 9
.Sh HISTORY
The
.Nm
series of functions first appeared in
.Nx 1.5 ,
and were later ported to
.Fx 4.6 .
This man page was updated with the information from
.Nx
.Nm
man page.
.Sh AUTHORS
.An -nosplit
The original
.Nx
.Nm
man page was written by
.An Bruce M. Simpson Aq Mt bms@FreeBSD.org
and
.An Darron Broad Aq Mt darron@kewl.org .