Figure 164 Header component variables

Table 16-1. Ethereal fields for 802.11 header components

802.11 header field

Ethereal field

Header fields

Duration

wlan.duration

Association ID

wlan.aid

Transmitter address

wlan.ta

Source address

wlan.sa

Receiver address

wlan.ra

Destination address

wlan.da

BSSID

wlan.bssid

Fragment number

wlan.frag

Sequence number

wlan.seq

Frame control subfields

Version

wlan.fc.version

Frame type

wlan.fc.type

Frame subtype

wlan.fc.subtype

ToDS flag

wlan.fc.tods

FromDS flag

wlan.fc.fromds

Fragment flag

wlan.fc.frag

Table 16-1. Ethereal fields for 802.11 header components

802.11 header field

Ethereal field

Retry flag

wlan.fc.retry

Power management flag

wlan.fc.pwrmgt

More Data flag

wlan.fc.moredata

WEP flag

wlan.fc.wep

Order flag

wlan.fc.order

WEP fields

Initialization vector

wlan.wep.iv

Key identifier

wlan.wep.key

Fields can be combined using operators. Ethereal supports a standard set of comparison operators: == for equality, != for inequality, > for greater than, >= for greater than or equal to, < for less than, and <= for less than or equal to. An example of a display filter would be wlan.fc.type==1 to match Control frames.

Logical operators and and or are supported; as in many programming languages, the exclamation point is used for logical negation. Boolean fields can be tested for existence, so Control frames with WEP enabled would be matched by the display filter wlan.fc.type==1 and wlan.fc.wep.

Figure 16-5 shows a complete 802.11 header in the tree view. Selecting the 802.11 header in the tree view highlights the bits that comprise the 802.11 header in the ASCII view at the bottom. Expanding the 802.11 header tree decodes all the fields in the 802.11 header.

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