Addressing in 802.11 Packets
Unlike Ethernet, best 802.11 packets absolutely accept three addresses, a
antecedent address, a destination address, and a Basic Service Set ID (BSSID).
The BSSID acreage abnormally identifies the AP and its accumulating of
associated stations, and is generally the MAC abode of the AP. The three
addresses acquaint the packets area they are going, who they came from, and
what AP to go through.
Not all packets, however, accept three addresses. Since it is so important
to abbreviate the aerial of sending ascendancy frames (such as
acknowledgments), the cardinal of $.25 acclimated is kept to a minimum. The
IEEE additionally acclimated altered agreement to call the addresses in
ascendancy frames. Instead of a destination address, ascendancy frames accept a
receiver address, and instead of a antecedent address, they accept a
transmitter address. The best accepted ascendancy anatomy is an acceptance
(ACK). Figure 3-4 shows the Wireshark adaptation of an ACK packet. Notice that
it has alone a distinct address, the receiver address. This is because an ACK
packet, by definition, acknowledges the aftermost packet sent. Unlike TCP,
there is no charge to analyze absolutely what is actuality acknowledged.
Figure 3-4: Wireshark adaptation of an ACK packet-notice it is alone 10
bytes
Figure 3-5 shows a archetypal abstracts packet. In this packet, the BSSID
and destination abode are the aforementioned because the packet was headed to
the Internet, and the AP was the gateway. If the packet had been destined for
addition apparatus on the aforementioned wireless network, the destination
abode would be altered than the BSSID.
Figure 3-5: Wireshark adaptation of a
abstracts packet
Sections
