The Atheros AR5000 chipset is the most commonly encountered chipset in 802.11a devices. This chipset combines the world's first 5 GHz "radio-on-a-chip" (RoC) and a host computer interface (baseband processor + MAC controller). It supports the Turbo Mode (72 Mbps theoretical speed) and hardware-based WEP encryption at 152 bits or less. Because it relies on a standard-process CMOS, both power consumption and the device costs are low, and the operational reliability is enhanced. AR5001x is a further evolution of AR5000 and is a common chipset in modern combo 802.11a/b/g cards.
Because we are interested in "hackable" drivers for 802.11a cards, which would let us monitor and inject traffic on a second layer, the most suited are Madwifi and Vantronix vt_ar5k drivers for Linux available from http://team.vantronix.net/ar5k/ and the Madwifi project at SourceForge. The list of vt_ar5k supported 802.11a cards includes Actiontec 802CA, Netgear HA501, Netgear HA311, Proxim Harmony, SMC 2735W, Sony PCWA-C500, IODATA WN-A54/PCM, and ICom SL-50. Unfortunately, the combo card support is not fully implemented yet and in our experience with vt_ar5k and Netgear 32-bit CardBus WAG511 and Orinoco Gold Combo cards the lead goes on and the card is detected, but the vt_ark5k module does not load. Nevertheless the supported card's vt_ar5k driver provides raw sniffing mode support and aims to implement frame injection in the future; stay tuned. Hopefully, by the time you hold this book in your hands, vt_ar5k combo card support is fully implemented.
Madwifi Linux drivers also provide support for 802.11a/b/g universal NIC cards based on the Atheros chipset. At the moment, these drivers are probably what you need to use for your 802.11a/b/g combo card under Linux. The official project is located at Sourceforge (http://sourceforge.net/projects/madwifi/). Additional information about madwifi drivers can be found at http://www.mattfoster.clara.co.uk/madwifi-faq.htm and Madwifi Wiki page http://madwifiwiki.thewebhost.de/wiki/. Before installing the modules, we recommend visiting these sites to get the latest details on the project and familiarize yourself with the FAQs.
Even though these drivers are in an early development state, they have been proven to work on many Atheros-based combo wireless cards. We have tested Proxim 8480-x and Netgear WAG511 and found them to work reasonably well at 18 to 24 mbits per second. Some people have reported performance, WEP, and power-management-related issues with Proxim 848x-based cards, so check the latest CVS source and patches section of the project page. Madwifi drivers are RFMON-friendly and are supported in the current versions of Kismet (see the kismet.conf file for more details).