WLAN(4) FreeBSD Kernel Interfaces Manual WLAN(4)


wlangeneric 802.11 link-layer support


device wlan


The wlan module provides generic code to support 802.11 drivers. Where a device does not directly support 802.11 functionality this layer fills in. The wlan module is required by all native 802.11 drivers as well as the ndis(4) support.

wlan supports multi-mode devices capable of operating in both 2.4GHz and 5GHz bands and supports numerous 802.11 standards: 802.11a, 802.11b, 802.11g, 802.11n, and 802.11s (Draft 3.0). The WPA, 802.11i, and 802.1x security protocols are supported through a combination of in-kernel code and user-mode applications. The WME/WMM multi-media protocols are supported entirely within the wlan module but require a suitably capable hardware device. Likewise the 802.11h specification is supported only by suitably capable devices.

Drivers provide 802.11 functionality through wlan interfaces that are created at runtime using interface cloning. This is done with the ifconfig(8) create command or using the wlans_IFX variable in rc.conf(5). Some drivers support the creation of multiple wlan interfaces that share the same underlying device; this is the way by which ``multi-bss support'' is provided but it can also be used to create WDS links and other interesting applications.

There are several types of wlan interfaces that may be created:

A client station in an infrastructure bss (i.e. one that associates to an access point).
An access point in an infrastructure bss.
A mesh station in an MBSS network.
A station in an IBSS network.
A station operating in ``adhoc demo mode''. This is essentially an IBSS station that does not use management frames (e.g. no beacons are transmitted). An ahdemo interface is especially useful for applications that want to transmit and receive raw 802.11 packets.
An interface used exclusively for capturing 802.11 frames. In particular this specified to have read-only properties which enables it to be operated on frequencies where one would otherwise not be allowed.
A station that passes 4-address 802.11 traffic for the purpose of tunneling traffic over a wireless link. Typically this station would share the same MAC address as a hostap interface. It may be possible to create wds interfaces without a companion hostap interface but that is not guaranteed; one may need to create a hostap interface that does not send beacon frames before wds interfaces may be created.

Note that an interface's type cannot be changed once it is created.

wlan defines several mechanisms by which plugin modules may be used to extend its functionality. Cryptographic support such as WEP, TKIP, and AES-CCMP are implemented as standalone modules (if not statically configured into a system) that register with wlan. Similarly there is an authenticator framework for defining 802.11 authentication services and a framework for integrating access control mechanisms specific to the 802.11 protocol.


If the IEEE80211_DEBUG option is included in the kernel configuration, debugging controls are available using:

sysctl net.wlan.X.debug=mask

where X is the number of the wlan instance and mask is a bit-or of control bits that determine which debugging messages to enable. For example,

sysctl net.wlan.0.debug=0x00200000

enables debugging messages related to scanning for an access point, adhoc neighbor, or an unoccupied channel when operation as an access point. The wlandebug(8) tool provides a more user-friendly mechanism for doing the same thing. Note that

sysctl net.wlan.debug=mask

defines the initial value of the debugging flags for each cloned wlan interface; this is useful to enable debug messages during interface creation.


The module name of wlan was used to be compatible with NetBSD.

Mesh stations follow the 802.11s Draft 3.0 specification which is not ratified and subject to change. Beware that this specification is incompatible with earlier drafts; and stations implementing earlier drafts (e.g. Linux) may not interoperate.


More information can be found in the IEEE 802.11 Standards.


The wlan driver first appeared in FreeBSD 5.0.


Atsushi Onoe is the author of original NetBSD software from which this work began. Sam Leffler brought the code into FreeBSD and then rewrote it to support multi-mode devices, 802.11g, 802.11n, WPA/802.11i, WME, multi-bss, and add the extensible frameworks for cryptographic, authentication, and access control plugins. This manual page was written by Tom Rhodes <trhodes@FreeBSD.org>.
February 22, 2012 FreeBSD