0001FIGURE 9-7 GATEWAY RESPONDS TO ARPTHAT ARP RESPONSE IS S...

Figure 9-7 Gateway Responds to ARP

That ARP response is sent back as a unicast message, so the switches in the path are going

to forward it directly to the port that leads back to the wireless client, rather than flooding

the frame out all ports. Eventually the frame is received by the WLC, and it must be re-

built as an 802.11 frame. When the WLC rewrites the frame, it places the DA as address 1,

the SA as address 3, and the TA as address 2, which is the SSID of the AP. Figure 9-8 illus-

trates this process.

As illustrated in Figure 9-9, the newly formed 802.11 frame is placed inside an LWAPP

header where the AP IP and MAC is the destination and the WLC IP and MAC is the

source. The LWAPP frame is forwarded to the AP.

Next, the AP must remove the LWAPP header, exposing the 802.11 frame. The 802.11

frame is buffered, and the process of sending a frame on the wireless network begins. The

AP starts a backoff timer and begins counting down. If a wireless frame is heard during

the countdown, the reservation in the heard frame is added to the countdown and the AP

continues. Eventually, the timer expires, and the frame can be sent an 802.11 frame.