![]() An HT mixed mode device must also send legacy format CTS-to-Self or RTS/CTS (Request to Send/Clear to Send) frames before transmitting. Specifically, HT mixed mode devices transmit a legacy format preamble, followed by an HT format preamble. To avoid this, the 802.11n standard also defines an HT mixed mode.Ī device using HT mixed mode prepares to transmit in both the old 802.11a/b/g fashion and the new 802.11n fashion. However, because an 802.11a/b/g device cannot tell that a Greenfield device is transmitting, it will go right ahead and transmit. Normally, 802.11 devices share channels by sensing when another device is transmitting, using a back-off timer to wait until the channel is free. Instead, their transmissions are likely to collide, causing errors and retransmissions for both parties. 802.11a/b/g devices cannot communicate with a Greenfield AP. ![]() You can then feed this file into your favorite network analyzer such as Wireshark to examine the traffic offline.Ī device that uses 802.11n high throughput (HT) mode - also known as Greenfield mode - assumes that there are no 802.11a/b/g stations using the same channel. ![]() This creates a file called airportSniffXXXXXX.cap in the /tmp directory, where XXXXXX is a string for uniqueness. ![]() You need to be an administrator (i.e., you need sudo privileges) to do this: Tell airport to sniff, and optionally provide a channel (which you now know thanks to your ability to scan). ![]() More awesome, perhaps, is the tool's ability to actually perform traffic sniffing and capture packets. $ airport en1 scan SSID BSSID RSSI CHANNEL HT CC SECURITY (auth/unicast/group) moscohome 00:22:6b:8b:86:51 -61 10 N - WPA2(PSK/AES/AES) PUBLIC-455H 00:15:6d:60:95:d1 -82 1 N - NONE Alex Network 00:1e:e5:24:c4:4f -86 1 Y TW WPA(PSK/TKIP,AES/TKIP) WPA2(PSK/TKIP,AES/TKIP) linksysELNIDO 00:21:29:a3:fd:99 -90 6 N - WPA(PSK/AES,TKIP/TKIP) WPA2(PSK/AES,TKIP/TKIP) 2WIRE024 00:18:3f:02:2f:49 -88 6 N US WEP 2WIRE940 00:12:88:d9:85:41 -93 6 N US WEPIf I wanted to see which of my neighbors still haven't upgraded from WEP, I could just filter using grep: ![]()
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