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Based on kernel version 4.8. Page generated on 2016-10-06 23:18 EST.

1	How to use packet injection with mac80211
2	=========================================
3	
4	mac80211 now allows arbitrary packets to be injected down any Monitor Mode
5	interface from userland.  The packet you inject needs to be composed in the
6	following format:
7	
8	 [ radiotap header  ]
9	 [ ieee80211 header ]
10	 [ payload ]
11	
12	The radiotap format is discussed in
13	./Documentation/networking/radiotap-headers.txt.
14	
15	Despite many radiotap parameters being currently defined, most only make sense
16	to appear on received packets.  The following information is parsed from the
17	radiotap headers and used to control injection:
18	
19	 * IEEE80211_RADIOTAP_FLAGS
20	
21	   IEEE80211_RADIOTAP_F_FCS: FCS will be removed and recalculated
22	   IEEE80211_RADIOTAP_F_WEP: frame will be encrypted if key available
23	   IEEE80211_RADIOTAP_F_FRAG: frame will be fragmented if longer than the
24				      current fragmentation threshold.
25	
26	 * IEEE80211_RADIOTAP_TX_FLAGS
27	
28	   IEEE80211_RADIOTAP_F_TX_NOACK: frame should be sent without waiting for
29					  an ACK even if it is a unicast frame
30	
31	 * IEEE80211_RADIOTAP_RATE
32	
33	   legacy rate for the transmission (only for devices without own rate control)
34	
35	 * IEEE80211_RADIOTAP_MCS
36	
37	   HT rate for the transmission (only for devices without own rate control).
38	   Also some flags are parsed
39	
40	   IEEE80211_RADIOTAP_MCS_SGI: use short guard interval
41	   IEEE80211_RADIOTAP_MCS_BW_40: send in HT40 mode
42	
43	 * IEEE80211_RADIOTAP_DATA_RETRIES
44	
45	   number of retries when either IEEE80211_RADIOTAP_RATE or
46	   IEEE80211_RADIOTAP_MCS was used
47	
48	 * IEEE80211_RADIOTAP_VHT
49	
50	   VHT mcs and number of streams used in the transmission (only for devices
51	   without own rate control). Also other fields are parsed
52	
53	   flags field
54	   IEEE80211_RADIOTAP_VHT_FLAG_SGI: use short guard interval
55	
56	   bandwidth field
57	   1: send using 40MHz channel width
58	   4: send using 80MHz channel width
59	   11: send using 160MHz channel width
60	
61	The injection code can also skip all other currently defined radiotap fields
62	facilitating replay of captured radiotap headers directly.
63	
64	Here is an example valid radiotap header defining some parameters
65	
66		0x00, 0x00, // <-- radiotap version
67		0x0b, 0x00, // <- radiotap header length
68		0x04, 0x0c, 0x00, 0x00, // <-- bitmap
69		0x6c, // <-- rate
70		0x0c, //<-- tx power
71		0x01 //<-- antenna
72	
73	The ieee80211 header follows immediately afterwards, looking for example like
74	this:
75	
76		0x08, 0x01, 0x00, 0x00,
77		0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
78		0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
79		0x13, 0x22, 0x33, 0x44, 0x55, 0x66,
80		0x10, 0x86
81	
82	Then lastly there is the payload.
83	
84	After composing the packet contents, it is sent by send()-ing it to a logical
85	mac80211 interface that is in Monitor mode.  Libpcap can also be used,
86	(which is easier than doing the work to bind the socket to the right
87	interface), along the following lines:
88	
89		ppcap = pcap_open_live(szInterfaceName, 800, 1, 20, szErrbuf);
90	...
91		r = pcap_inject(ppcap, u8aSendBuffer, nLength);
92	
93	You can also find a link to a complete inject application here:
94	
95	http://wireless.kernel.org/en/users/Documentation/packetspammer
96	
97	Andy Green <andy@warmcat.com>
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