How does opportunistic key caching speed up the roaming process?

A.
When SNR of a station begins to drop, it pre-authenticates with neighboring APs, which cache
the pair wise master key of the station for a user-defined amount.

B.
When a station authenticates, the AP sends encryption keys to the controller, which distributes
them to all APs in the mobility domain.

C.
When a station decides to roam, it notifies its AP, which then distributes the pair wise master
key of the stations to APs in its mobility domain.

D.
After a station authenticates with an AP, it pre-authenticates with neighboring APs, which cache
the pair wise master key in case the station later roams.

Explanation:

Student Guide Book 1 – Implementing and Troubleshooting HP Wireless Networks – Page 3-77
To reduce this latency, an MSM Mobility or Premium Mobility Controller appliesopportunistic key
caching. When a client sends a disassociation frame to its AP tosignal that is going to roam away
from it, the AP sends the client‘s key (moreprecisely, its pairwise master key [PMK], as you will
learn in the next module) toneighboring APs through the backed Ethernet network. The new AP
receives theclient‘s association request. Rather than implement the full 802.1X
authenticationprocess, the AP proceeds directly to a brief handshake in which it verifies that
theclient is using the correct PMK. The client must also support opportunistic key cachingso that it
keeps the key for the new association.
Answers B and C are supposed to be correct, if WPA PSK is used all APs know PMK, if 802.1x
when clientrequest roam away the AP inform PMK to neighbors APs.