Wireless overview

This article deals with 802.11 wireless. OpenWrt supports other wireless devices too, see Bluetooth, 802.15.4 (r45348) or RTL-SDR (RTL-SDR on TL-WR703n)

Linux Wireless is the source for documentation regarding the entire Linux Kernel IEEE 802.11 (“wireless”) subsystem. It is a wiki like this one, so feel free to contribute there as well! Everything not OpenWrt specific belongs there. This page is an exception, as I believe I can provide a better introduction.

• IEEE 802.3 is a family of communication protocols comprising Layer 1 and Layer 2 Sublayer MAC
• IEEE 802.3 has an official name: Ethernet
• IEEE 802.11 is a family of communication protocols also comprising Layer 1 and Layer 2 Sublayer MAC
• IEEE 802.11 has no official name, so most people simply call it “wireless” or “wavelan” or wifi (note that Wi-Fi is a brand name)
• The support for IEEE 802.11 in the Linux kernel is fragmented. This means there are two frames (WEXT=deprecated, cfg80211 + nl80211=current) and multiple drivers, e.g.
  • For some Broadcom WNICs, there are also three drivers available: Broadcom proprietary drivers (broadcom-wl), broadcom mac80211-based drivers (the b43) and the brcmSmac- and brcmFmac drivers
    • To set up and configure, wireless utilities are available, however on OpenWrt, UCI is preferred: /etc/config/wireless and /etc/config/network.
  • There are two different types of WNICs to distinguish: SoftMAC and FullMAC devices; also see About mac80211.
• Many drivers might require firmware blobs. Most firmware code is closed source. (Exception carl9170, ath9k_htc)
• Atheros ath9k does not require firmware.
• In contrast to Ethernet drivers, wireless drivers work in a Wireless Mode of Operation.

→Wireless Modes of Operation →Kernel: Wireless Modes of Operation

See what the Linux 802.11 driver for your hardware can and cannot do. Some drivers support only one mode: STA (also called station, client or managed mode) other drivers support multiple modes, some even simultaneously (interface combination):

• →wireless.kernel.org: Driver capabilities: support for Wireless Modes of Operation
  
• →Wikipedia: Driver capabilities: support for Wireless Modes of Operation

Limitations when combining multiple wireless modes of operation at the same time do exist.

• →Driver limitations when combining multiple wireless modes of operation

Firmware Limitations do exist

• →No 5GHz AP with Intel 7260

Available frequencies, bands and channels are subject to regulation in each state. Please see: https://git.kernel.org/pub/scm/linux/kernel/git/sforshee/wireless-regdb.git/tree/db.txt

Wireless drivers are pulled on a more or less regular basis from wireless-testing and the OpenWrt patches which are not mainlined yet are adjusted, see e.g. r36939. OpenWrt does not use kernel drivers. The package is called mac80211.

• history of commits to OpenWrt trunk regarding mac80211
• tickets on mac80211, better is a custom query in Trac: e.g. custom query

Similar work (brand new drivers for older kernel) is done by the backports project April 2013 announcement, previously called compat-wireless or compat-driver. OpenWrt does not use this, despite referencing it by name.

• Wireless Utilities

• kismet – An IEEE 802.11 network detector, sniffer and intrusion detection system.
• aircrack-ng – Aircrack-ng is the next generation of aircrack with new features
• horst – A scanning and analysis tool for IEEE 802.11 networks and especially IBSS (ad-hoc) mode and mesh networks (OLSR).

This shall be, but is not, an exhaustive list of all packages in the OpenWrt repository regarding wireless stuff to play with. The installation is always the same opkg install <package>. For documentation regarding the configuration and utilization, search for Howtos in this wiki or in the Internet.

E.g.:

Due to r31954 tweaking the regulatory.bin to enable channel 13 and 14 is no longer an option.

You can find a couple of probed scenarios under → wifi section.

• problem with any kinds of multicast traffic on 802.11 networks

• on AP modes
• r37553 add authsae open80211s authentication daemon IEEE 802.11s
• r37483 ath9k: add initial tx queueing rework patches This forces all packets (even for un-aggregated traffic) through software queues to improve fairness and stability

• → OpenWrt Wireless FAQ