Iuwne10 S02 L03

© 2008 Cisco Systems, Inc. All rights reserved. IUWNE v1.0—2-1

Basic Cisco WLAN Installation

Discovering and Associating with a Controller


LWAPP ModesLightweight Access Point Protocol


Layer 3 Lightweight AP Protocol (LWAPP)

Layer 3 LWAPP is in a UDP/IP frame

Cisco WLAN controller and AP can be connected to the same VLAN/subnetwork or connected to a different VLAN/subnetwork

Requires Cisco AP to obtain an IP address using DHCP

Control traffic is encrypted, data is not


Controller > General


Access Point Association Sequence


AP LWAPP Discover and Join Overview

AP issues a DHCP DISCOVER to obtain address

AP attempts Layer 2 controller discovery

AP attempts Layer 3 controller discovery– LWAPP discovery broadcast on local subnet

– Over-the-Air provisioning (OTAP)

– Local stored controller IP address from prior successful join process

– DHCP option 43

– DNS resolution of CISCO-LWAPP-CONTROLLER

After AP discover controllers, it selects and joins one via primary, secondary, tertiary, or master configuration of controllers


AP LWAPP Discovery

AP obtains an IP address

– Statically defined

– DHCP discover

AP tries to connect to a controller using Layer 2 then Layer 3 LWAPP (LWAPP only models), or Layer 3 LWAPP (Cisco IOS-based models)

Layer 3 LWAPP discovery order:

– Subnetwork broadcast mode

Connect Cisco AP directly to, or same subnet as, a Cisco controller to learn Cisco controller IP address

Cisco AP will send a subnetwork broadcast


AP LWAPP Discovery (Cont.)

Over-the-air provisioning (OTAP)

– Connect Cisco AP in range of another already connected AP

– Configure the controller to allow OTAP

– Cisco AP will receive information about controllers from its neighboring APs

AP priming

– Connect Cisco AP directly, or same subnet as a Cisco controller to learn Cisco controller mobility group IP addresses

– Move Cisco AP to a remote network and have it use DHCP for a local and gateway address

– Cisco AP will send a subnetwork broadcast discovery request to the primary controller and all controllers in the learned mobility group


LWAPP Layer 3 Discovery

DHCP vendor option mode

– Place Cisco AP on remote network and have it use DHCP for a local and gateway address

– Use DHCP extension to learn a Cisco controller management interface IP address from extension Option 43

DNS/DHCP vendor option mode

– Place Cisco AP on remote network and have it use DHCP for a local and gateway address

– Use DHCP extension to learn a DNS IP address

– Cisco AP will then make an address resolution call using the hostname CISCO-LWAPP-CONTROLLER, which should be configured to return the management interface IP address of available controllers


Access Point Join Order

Response from primary, then secondary, and finally tertiary configured controller

If no configured controller, response from a master controller

If no master controller response, response from the least loaded controller

Least loaded AP-Manager interface or least loaded controller


Access Point Join PhaseWithout Master


Access Point Join Phase Without Master (Cont.)


Access Point Join PhaseWithout Master (Cont.)


Access Point Join PhaseWith Master


Access Point Join Phase With Master (Cont.)


Access Point Join PhaseWith Master (Cont.)


Primary Controller Name


Controller > Advanced > Master Controller Mode

Master controller configuration should only be used for provisioning APs to associate them to a particular controller and then to assign a primary controller.


AP LWAPP Join Messages

LWAPP join request Includes type of controller and MAC address of controller Includes AP hardware and software version Includes the name of the AP issuing the join request Indicates the number and type of radios present in AP Includes a certificate payload for establishing a secure connection Includes a session payload to setup the session value Includes a test payload to test the ability of the network to support

jumbo frames

LWAPP join reply Includes a result code Includes controller’s certificate payload response Includes a test payload to test the network’s ability to support

jumbo frames


AP States


LWAPP Configuration Phase

The LWAPP configure request: Wants the controller to provide configuration data

Provides the controller with a list of configurable parameters and the current values

The LWAPP configure response: Provides configuration values for the AP

Allows the controller to override requested configuration elements from the AP.

Includes configure command packets.

Causes the AP:

– To evaluate each configuration element

– To begin implementing the configuration elements


Design: AP Redundancy

AP redundancy RF “self-healing” allows system to compensate dynamically for lost APs

System must be designed to support self-healing

Distance between APs determines redundancy limits


Controller Redundancy


Controller Redundancy Designs—N + 1


Controller Redundancy Designs—N + N


Controller Redundancy Designs—N + N + 1


Summary

LWAPP can operate at Layer 2, using Ethernet or Layer 3, using IP.

An LWAPP AP will try to discover as many controllers as possible, using Layer 2 or Layer 3 methods.

It will then choose to join the best controller, based on configuration or network elements.

Once associated to a controller, it will receive its configuration using a secure connection.

A good design should plan for AP redundancy but also controller redundancy.

Iuwne10 S02 L03

Technology

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