Chap 19 - Wireless Roaming and Location Svcs

Question 1

What is Intracontroller Roaming?

Answer 1

When a client roams between LWAPs connected to the same WLC.

Question 2

How long does an Intracontroller Roam take?

Answer 2

Less than 10 msec

Question 3

What 2 things might happen when a wireless client re-associates?

Answer 3

• Client might renew its DHCP IP address assignment
• Client might need to re-authenticate (802.1x)

Question 4

What 3 techniques do controllers offer to streamline key exchanges during roam?

Answer 4

• Cisco Centralized Key Management (CCKM)
• Key caching
• 802.11r

Question 5

What is Cisco Centralized Key Management (CCKM)

Answer 5

One controller maintains a database of clients and keys on behalf of its APs and provides them to other controllers and their APs as needed during client roams.

Question 6

What is Key Caching?

What is it?
What are 2 limitations?

Answer 6

• Each client maintains in cache a list of keys used with prior AP associations and presents them as it roams. The destination AP must be present in this list.
• The list is limited to key entries from 8 prior APs.
• Client must have a supplicant

Question 7

What is 802.11r ?

How does this help a client roam?
What else can the client maintain?
What does the client need to have?

Answer 7

• Client caches a portion of the authentication server’s key and presents that to future APs as it roams. This makes roaming much faster.
• The client can also maintain its QoS parameters as it roams
• Client must have supplicant

Question 8

What is Intercontroller Roaming?

Answer 8

Roaming between APs on different controllers

Question 9

What is a Intercontroller Layer 2 roam?

What stays the same on the client?
How long does this roam take?

Answer 9

• Client roams but stays on the same VLAN and Subnet
• Client keeps same IP address
• Fast - less than 20 msec (10 msec for Intracontroller roam)

Question 10

What happens in a Layer 3 Roam?

Answer 10

• Client roams to different AP w/different controller that is on a different subnet *
• Original controller (anchor controller) and Foreign controller build a CAPWAP tunnel
• Client keeps original IP and client’s data flows across the CAPWAP tunnel

Question 11

What advantage do Mobility Groups provide and what 4 things are supported?

Answer 11

• Clients can roam quickly between controllers in the same Mobility Group.
• Layer 2 and Layer 3 roaming
• CCKM
• Key caching
• 802.11r credential caching.

Question 12

What is true if a client roams between controllers not in the same mobility group?

Answer 12

Credentials are not cached and shared so clients must go through a full authentication during the roam.