12. Roaming

Question 1

When a client roams in between 2 autonomous APs, what does the AP do with any leftover wireless frames after the client has left?

Answer 1

It forwards them to the new AP over the wired infrastructure because that’s where the clients’ MAC address now resides.

Question 2

Roaming between two APs that are joined to the same controller is called what?

Answer 2

Intracontroller roaming.

10ms

Question 3

What are the three techniques, Cisco controllers offer, to minimize the time and effort spent on key exchanges during roams?

Answer 3

1. Cisco Centralized Key Management (CCKM)
2. Key caching
3. 802.11r

Question 4

What does the client have to support to utilize CCKM during roaming?

Answer 4

Cisco Compatible Extensions (CCX)

Question 5

How does CCKM work?

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.

Question 6

When roaming what is key caching?

Answer 6

Client maintains a list of keys used with prior AP associations and presents them as it roams.

Question 7

How does 802.11r help a client when roaming?

Answer 7

The client can cache a portion of the authentication server’s key and presents that to future APs as it roams.

Question 8

Roaming between two APs that are joined to different controller is called what?

Answer 8

Intercontroller roaming

Question 9

What is a layer 2 intercontroller roam?

Answer 9

When a client roams between APs on different controllers but the WLANs are on the same VLAN
(20ms)

Question 10

What’s another name for layer 2 intercontroller?

Answer 10

Local-to-local roam

Question 11

How is a client able to maintain its IP address when roaming to an AP on a different controller and a different VLAN?

Answer 11

There is a CAPWAP tunnel maintained between the controllers.

Question 12

In a layer 3 intercontroller roam, what is the controller called that maintains connectivity to the original VLAN?

Answer 12

Anchor controller

Question 13

In a layer 3 intercontroller roam, what is the controller called that has the AP currently associated with the client?

Answer 13

Foreign controller

Question 14

In order for controllers to execute a layer 2 or layer 3 roam between them, them must both be in what type group?

Answer 14

Mobility group

Question 15

Why might a client have to do a full authentication when doing an intercontroller roam?

Answer 15

The controllers are not in the same mobility group.

Question 16

What is the difference between a mobility domain and a mobility group?

Answer 16

It is a hierarchy. There are mobility groups within a mobility domain.

Question 17

How many controllers can be in a mobility domain and how many in a mobility group?

Answer 17

72 in domain

24 in group

Question 18

There are two distinct roles and functions involving mobility. What are the functions of a mobility controller (MC)?

Answer 18

Manages roaming
Performs RRM
Performs wireless IPS
Manages guest access

Question 19

There are two distinct roles and functions involving mobility. What are the functions of a mobility agent (MA)?

Answer 19

Terminates CAPWAP tunnels
Maintains client database
Enforces security and QoS policies

Question 20

In reference to mobility, there are two roaming coordination roles that exist from the client’s perspective. What are they?

Answer 20

Point of Presence (PoP) - IP address, security policies

Point of Attachment (PoA) - association, QoS

Question 21

List the roaming hierarchy on converged controllers?

Answer 21

Mobility domain
Mobility group
Mobility subdomain
Switch peer group (SPG)

Question 22

In converged controller roaming, whrere is the most efficient roaming happening?

Answer 22

When it’s with the same SPG

Question 23

Each WCM functions as a MA but must be joined to an MC. Can a WCM function as an MC?

Answer 23

Yes