11. Controller Discovery Flashcards
What are the most common AP states in their sequence order?
- AP boots
- WLC discovery
- CAPWAP tunnel
- WLC join
- Download image
- Download config
- Run
- Reset
During the CAPWAP tunnel state the AP and WLC authenticate each other using what method?
The exchange digital certificates.
Under what circumstances might an AP need to download a new code image?
AP joins a WLC but doesn’t have the same version of code.
A code upgrade is performed on the WLC and all assocate AP will need to download the new code.
WLC fails, causing the AP to join another WLC which doesn’t have the same code.
The goal of the WLC discovery state is to build a list of live candidate controller using what methods?
Prior knowledge of WLCs
DHCP and DNS info
Broadcast on the local subnet
To discover a WLC, an AP send what kind of frame over what port?
CAPWAP Discovery Request over UDP port 5246
WLC send back a CAPWAP Discovery Response
What is the sequence of WLC discovery process?
- Broadcast on local subnet
- Use locally stored WLC addresses
- Use DHCP
- Use DNS
- If none of the steps have worked the AP resets and starts the process all over.
An AP can be “primed” with how many controllers which are stored in non-volatile memory?
Three - primary, secondary, and tertiary.
An AP should a save up to how many controllers that have been previously joined?
Eight
Which DHCP option can suggest a list of WLC addresses?
Option 43
When discovering WLCs, an AP will try to resolve what name using DNS?
CISCO-CAPWAP-CONTROLLER.localdomain
What are the steps in the WLC selection process (deciding which controller to join)?
- Try primed addressed in succession
- Try the master controller (discovered thru broadcast)
- Try the least-loaded controller (during discovery phase controllers report their load)
What is the purpose of APs having a priority value?
If a controller reaches its capacity and an additional AP try to join, the controller tries to accommodate as man higher priority APs as possible.
What are the available settings for an APs priority value?
Low
Medium
High
Critical
Will an AP that has failovered to the secondary controller, move back to the primary controller once it’s available?
Normally no. You would have to globally enable the AP Fallback feature.
What is the default keep alive time being sent by the AP?
30 seconds
The AP expects a response from the controller to its keep alive. What happens if it does not get a response to its normal keep alive message?
By default it sends 4 keep alive messages at 3 second intervals. If it still doesn’t hear a reply, it will join another controller.
What is N + 1 redundancy for controllers?
N stands for how ever many controllers you have which are taking load. Add one controller without any load to have a failure from the other controllers.
What is N + N redundancy for controllers?
You pair controllers up and share the load of APs keeping them under 50% load so they can handle all APs if the other controller fails fails.
What is N + N + 1 redundancy for controllers?
You pair controllers up as primary and secondary and the have an extra controller without load in case both controllers in a pair fail it would go the the extra listed as tertiary controller.
What is SSO redundancy for controllers?
Stateful switchover
Controllers are paired with one active and one standby
What is the benefit of SSO redundancy?
APs do not have to go thru selection process and the failover is very rapid.
What UDP or TCP port numbers do CAPWAP control and data tunnels use?
Control - UDP 5246
Data - UDP 5247
What UDP or TCP port numbers do the Cisco Miraki APs use to communicate to the cloud?
RF reporting - UDP 7351
Configuration management - TCP 7334
