This is not an in-depth post on 802.11r. Instead, it is just about one piece of the 802.11r puzzle that will hopefully remain in my brain long enough for certification and beyond!
For a detailed review of 802.11r, I suggest Devin Akin’s excellent white paper:
I was having trouble understanding the difference between two of the wpa_cli commands ft_ds and roam. The wpa_cli is the WPA command line interface for interacting with wpa_supplicant (as a station in client mode).
The wpa_cli command help gave me a clue, but wasn’t giving me the full story:
ft_ds = request over-the-DS FT with
roam = roam to the specified BSS
So I setup a Cisco testbed with a WLC2504 and two 1602 APs. Then setup a LANforge-WiFIRE test system with a client to roam between the two APs and with a separate monitor interface for packet captures.
With the wpa_cli ft_ds command I obtained the following capture:
With the wpa_cli roam command I obtained the following capture:
Staring at the packet captures and re-reading the following helped me see the difference:
• STA communication to the target AP via current AP using FT Action frames.
• STA communicates directly with the target AP using FT Authentication frames.
The command wpa_cli ft_ds dc:a5:f4:ff:4f:af initiates a FT Request (Action Frame) from the station 00:0e:8e:43:3a:71 to the target AP dc:a5:f4:ff:4f:af via the current AP dc:a5:f4:f3:ce:9f that the station is connected to.
The command wpa_cli roam dc:a5:f4:ff:4f:af initiates a FT Authentication from the station 00:0e:8e:43:3a:71 over the air directly to the target AP dc:a5:f4:ff:4f:af.
Both commands initiate an 802.11r Fast BSS Transition, but the distinction between the two is important to understanding how clients will transition. Using this command is a helpful way to test 802.11r wireless network setups and verifying that when it comes time for real clients to roam, you will have some confidence that it will work as expected.