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We can understand all possible ways of wireless communication in four cases in the following ways :
Case 1: we talk of AP to AP communication
Case 2: we talk of client to client communication (when AP is involved) : from wireless to the AP
Case 3: we talk of client to client communication (when AP is involved) : from AP to the wireless
Case 4: we talk of client to client communication (when no AP is involved)
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In Wireshark :
To filter all frames pertaining to case 1, use filter as wlan.fc.ds == 0x11
To filter all frames pertaining to case 2, use filter as wlan.fc.ds == 0x10
To filter all frames pertaining to case 3, use filter as wlan.fc.ds == 0x01
To filter all frames pertaining to case 4, use filter as wlan.fc.ds == 0x00
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These four cases are represented via bits in the following way :
wlan.ra wlan.ta
Receiver Transmitter
To DS <- From DS
Case 1: 1 1 either do move To DS or move From DS) ie, AP to AP communication, as in Mesh Setup.
Case 2: 1 0 Specific wireless client to AP
Case 3: 0 1 AP !to all wireless clients but specific wirless client
Case 4: 0 0 or do not move To DS or move From DS) ie, AP to all wireless clients (broadcast)
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IF
1 indicates AP (bssid)
0 indicates WirelessClient (w/c)
THEN
Destination<- Source
Receiver <- Transmitter
filter wlan.fc.ds == 0x 1 1 will indicate the traffic in the direction AP <- AP
filter wlan.fc.ds == 0x 1 0 will indicate the traffic in the direction w/c <- AP
filter wlan.fc.ds == 0x 0 1 will indicate the traffic in the direction AP <- w/c
filter wlan.fc.ds == 0x 0 0 will indicate the traffic in the direction w/c <- w/c (without AP)
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Legend:
w/c1: first wireless client
w/c2: second wireless client
src : when client is the source of communication.
dst : when client is the destination of communication.
! means "not"
Say, there are two wireless clients talking , where first wireless client sends message to the second wireless client
Address 1 Address 2 Address 3 Address 4
Receiver Transmitter Destination Source
1 1 AP2(bssid) AP1(bssid) w/c2 w/c1
1 0 w/c2(dst) AP (bssid) w/c1(src)
0 1 AP (bssid) w/c1(src) w/c2(dst)
0 0 w/c2(dst) w/c1(src) AP (bssid)
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In other words, the same information can be understood in the following ways:
In wireless communication, we talk on terms of wireless clients and Access Points ( known as DS )
(A) Wireless Communication Types:
AP to AP communication.
Client to Client communication. (either when AP is involved or AP is not involved)
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(B) So, there comes out to be four subtypes of wireless communication:
if ( AP - AP ) Case 1: (when in mesh mode)
if ( client-client ){
if ( AP is involved){
if (wireless to AP) Case 2:
if (AP to Wireless) Case 3:
}
if (!AP is involved) Case 4: (ad-hoc n/w )
}
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(C)
Wireless frames are always sent from a transmitting device to a receiving device.
( while reaching all the way to the final destination )
RA - indicates the address of the device, to which transmission of frame should be sent, so that the Final Destination can get it.
TA - indicates the address of the device, which transmitted the data ( not necessarilly, the originator of the transmitted data, who actually transmitted the frame
)
Address1 field always contains the RA. wlan.ra
Address2 field always contains the TA. wlan.ta
-if (bridges in use ) {Address 4 is used }
-else
if ( RA is not the final recipient ) { Address 3 contains the final Destination Address }
if ( RA is the final recipient ) { Address 3 contains the RA}
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