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+How to use packet injection with mac80211
+=========================================
+
+mac80211 now allows arbitrary packets to be injected down any Monitor Mode
+interface from userland.  The packet you inject needs to be composed in the
+following format:
+
+ [ radiotap header  ]
+ [ ieee80211 header ]
+ [ payload ]
+
+The radiotap format is discussed in
+./Documentation/networking/radiotap-headers.txt.
+
+Despite many radiotap parameters being currently defined, most only make sense
+to appear on received packets.  The following information is parsed from the
+radiotap headers and used to control injection:
+
+ * IEEE80211_RADIOTAP_FLAGS
+
+   IEEE80211_RADIOTAP_F_FCS: FCS will be removed and recalculated
+   IEEE80211_RADIOTAP_F_WEP: frame will be encrypted if key available
+   IEEE80211_RADIOTAP_F_FRAG: frame will be fragmented if longer than the
+			      current fragmentation threshold.
+
+ * IEEE80211_RADIOTAP_TX_FLAGS
+
+   IEEE80211_RADIOTAP_F_TX_NOACK: frame should be sent without waiting for
+				  an ACK even if it is a unicast frame
+
+ * IEEE80211_RADIOTAP_RATE
+
+   legacy rate for the transmission (only for devices without own rate control)
+
+ * IEEE80211_RADIOTAP_MCS
+
+   HT rate for the transmission (only for devices without own rate control).
+   Also some flags are parsed
+
+   IEEE80211_RADIOTAP_MCS_SGI: use short guard interval
+   IEEE80211_RADIOTAP_MCS_BW_40: send in HT40 mode
+
+ * IEEE80211_RADIOTAP_DATA_RETRIES
+
+   number of retries when either IEEE80211_RADIOTAP_RATE or
+   IEEE80211_RADIOTAP_MCS was used
+
+ * IEEE80211_RADIOTAP_VHT
+
+   VHT mcs and number of streams used in the transmission (only for devices
+   without own rate control). Also other fields are parsed
+
+   flags field
+   IEEE80211_RADIOTAP_VHT_FLAG_SGI: use short guard interval
+
+   bandwidth field
+   1: send using 40MHz channel width
+   4: send using 80MHz channel width
+   11: send using 160MHz channel width
+
+The injection code can also skip all other currently defined radiotap fields
+facilitating replay of captured radiotap headers directly.
+
+Here is an example valid radiotap header defining some parameters
+
+	0x00, 0x00, // <-- radiotap version
+	0x0b, 0x00, // <- radiotap header length
+	0x04, 0x0c, 0x00, 0x00, // <-- bitmap
+	0x6c, // <-- rate
+	0x0c, //<-- tx power
+	0x01 //<-- antenna
+
+The ieee80211 header follows immediately afterwards, looking for example like
+this:
+
+	0x08, 0x01, 0x00, 0x00,
+	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
+	0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
+	0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
+	0x10, 0x86
+
+Then lastly there is the payload.
+
+After composing the packet contents, it is sent by send()-ing it to a logical
+mac80211 interface that is in Monitor mode.  Libpcap can also be used,
+(which is easier than doing the work to bind the socket to the right
+interface), along the following lines:
+
+	ppcap = pcap_open_live(szInterfaceName, 800, 1, 20, szErrbuf);
+...
+	r = pcap_inject(ppcap, u8aSendBuffer, nLength);
+
+You can also find a link to a complete inject application here:
+
+http://wireless.kernel.org/en/users/Documentation/packetspammer
+
+Andy Green <andy@warmcat.com>