Hostapd簡介：
簡單說，hostapd能夠使得無線網卡切換爲master模式，模擬AP(通常可以認爲是路由器)功能，也就是我們說的軟AP(Soft AP)。
Hostapd的功能就是作爲AP的認證服務器，負責控制管理stations(通常可以認爲帶無線網卡的PC)的接入和認證。
通過Hostapd可以將無線網卡切換爲AP/Master模式，通過修改配置文件，可以建立一個開放式的(不加密)的，WEP，WPA或WPA2的無線網絡。並且通過修改配置文件可以設置無線網卡的各種參數，包括頻率，信號，beacon包時間間隔，是否發送beacon包，如果響應探針請求等等。還可以設置mac地址過濾條件等。具體可以參考它的配置文件說明。
下面就從官網上摘下的部分原因及翻譯。翻譯的不好請見諒。
hostapd is an IEEE 802.11 AP and IEEE 802.1X/WPA/WPA2/EAP/RADIUS Authenticator.
Hostapd是IEEE 802.11 AP and IEEE 802.1X/WPA/WPA2/EAP/RADIUS的認證器
hostapd is a user space daemon for access point and authentication servers. It implements IEEE 802.11 access point management, IEEE 802.1X/WPA/WPA2/EAP Authenticators, RADIUS client, EAP server, and RADIUS authentication server. The current version supports Linux (Host AP, madwifi, mac80211-based drivers) and FreeBSD (net80211).
Hostapd是一個訪問點以及認證服務器的運行於用戶空間的守護程序。它實現了IEEE 802.11接入帶你(Access Point)的管理功能，是IEEE 802.1X/WPA/WPA2/EAP的認證器,是 RADIUS client, EAP server, and RADIUS認證服務器。當前版本的hostapd支持linux上Host AP，madwifi和基於mac80211協議棧的驅動程序，以及FreeBSD上net80211協議棧的驅動程序。
hostapd is designed to be a "daemon" program that runs in the background and acts as the backend component controlling authentication. hostapd supports separate frontend programs and an example text-based frontend, hostapd_cli, is included with hostapd.
Hostapd是一個後臺守護進程，作爲後臺組件來控制和管理認證功能。Hostapd支持多個前臺程序。hostapd_cli，就是一個跟hostapd一起的命令行前臺程序。
支持特性
Supported WPA/IEEE 802.11i/EAP/IEEE 802.1X features
支持WPA/IEEE 802.11i/EAP/IEEE 802.1X
- WPA-PSK ("WPA-Personal")
- WPA with EAP (with integrated EAP server or an external RADIUS backend authentication server) ("WPA-Enterprise")
- key management for CCMP, TKIP, WEP104, WEP40
- WPA and full IEEE 802.11i/RSN/WPA2
- RSN: PMKSA caching, pre-authentication
- IEEE 802.11r
- IEEE 802.11w
- RADIUS accounting
- RADIUS authentication server with EAP
- Wi-Fi Protected Setup (WPS)
- Supported EAP methods (integrated EAP server and RADIUS authentication server)
- EAP-TLS
- EAP-PEAP/MSCHAPv2 (both PEAPv0 and PEAPv1)
- EAP-PEAP/TLS (both PEAPv0 and PEAPv1)
- EAP-PEAP/GTC (both PEAPv0 and PEAPv1)
- EAP-PEAP/MD5-Challenge (both PEAPv0 and PEAPv1)
- EAP-TTLS/EAP-MD5-Challenge
- EAP-TTLS/EAP-GTC
- EAP-TTLS/EAP-MSCHAPv2
- EAP-TTLS/MSCHAPv2
- EAP-TTLS/EAP-TLS
- EAP-TTLS/MSCHAP
- EAP-TTLS/PAP
- EAP-TTLS/CHAP
- EAP-SIM
- EAP-AKA
- EAP-AKA'
- EAP-PAX
- EAP-PSK
- EAP-SAKE
- EAP-FAST
- EAP-IKEv2
- EAP-GPSK
Following methods are also supported, but since they do not generate keying material, they cannot be used with WPA or IEEE 802.1X WEP keying.
同樣支持下面的這些功能，但是這些不生成建鑰資料，所以它們不能夠WPA 或者 IEEE 802.1X WEP一同使用
- EAP-MD5-Challenge
- EAP-MSCHAPv2
- EAP-GTC
- EAP-TNC (Trusted Network Connect; TNCS, IF-IMV, IF-T, IF-TNCCS)
支持的無線網卡/驅動
- Linux mac80211 drivers
- Host AP driver for Prism2/2.5/3
- madwifi (Atheros ar521x)
- BSD net80211 layer (e.g., Atheros driver) (FreeBSD 6-CURRENT)
如何確定一款無線網卡是否能被hostpad支持
以ubuntu10.04爲例
執行sudo aptitude install iw，安裝無線配置工具iw
執行iw list，如果在下面的結果中出現AP字樣，那麼就表示這款網卡支持hostapd
Supported interface modes:
* IBSS
* managed
* AP
* AP/VLAN
* WDS
* monitor
* mesh point
推薦網址
http://hostap.epitest.fi/hostapd/
http://wireless.kernel.org/en/users/Documentation/hostapd
https://help.ubuntu.com/community/WifiDocs/MasterMode
http://hostap.epitest.fi/gitweb/gitweb.cgi?p=hostap.git;a=blob_plain;f=hostapd/hostapd.conf
