NIS Chapter 06

Question 1

What is roaming?

Answer 1

is when a STA switches APs while maintaining network connectivity for the upper layer applications

Question 2

In what layer does roaming happen?

Answer 2

It happens in layer 2 and is known as the reassociation service

Question 3

What causes the client station to roam?

Answer 3

propriety rules written into the AP that are defined as the received signal strength indicator threshold. With that it will initiate the roaming process.

Question 4

What is the primary tasks of the AP to AP handoff?

Answer 4

1. target ap tells original that the client is roaming
2. target asks original for buffered client packets

Question 5

What are 2 problems with the autonomous AP-AP?

Answer 5

• back end communication depend on the vendor since it is propierty. AP comm not very effective
• handoffs very slow

Question 6

WHat does RSNA say about roaming clients?

Answer 6

New and unique keys must be generated every time a client roams

Question 7

What are the 3 steps that lead to the creation of a PMK (regardless of PSK or 802.1X/EAP

Answer 7

1. discovery
2. create PMK
3. 4 way handshake

Question 8

Recap all the pre to the generation of PTK

Answer 8

3 steps

Question 9

What is PMKSA?

Answer 9

this is the result of a successful authentication success between supplicant and AS

Question 10

Name the types of OMKSA that an PMKID can reference

Answer 10

1. PMK association from a PSK from the target AP
2. cached PMKSA from 802.1X/EAP
3. Cahsed and obtained through preauth w

Question 11

What is preauth?

Answer 11

A client can use preauth to establish a new PMKSA . It allows a STA to initiate a 802.1X/EAP exchange with a radius server while it is still associated with the original AP

Question 12

What is PMK caching

Answer 12

• this is a method used by AP and STA to maintain a PMKSA while a client roams . Where the client and authenticator cache PMKs. The PMKIDs are then used to skip the 802.1X authentication and go to the 4 way handshake. The PMK that already exists will then be used as seeding for 4 way.

Question 13

Why is OKC (oppurtinistic key caching) the preffered method?

Answer 13

PMK caching and preauth dp not scale well

Question 14

What makes OKC scale better?

Answer 14

caching PMK amongst multiple APs under some admin control

Question 15

what is the formula for the P<KID of the OKC?

Answer 15

hmac-sha1-128(PMK, pmk name || AA|| SPA)

Question 16

summarise the process of OKC

Answer 16

-

Question 17

what are the advantages of OKC over preauth and cache?

Answer 17

• reduce load on radius sever
• only one PMK