Cisco Unified Wireless Network Administration: AP Association Finding a Controller Cisco Unified Wireless Network Administration: AP Association - Finding a Controller 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-1 Lesson Overview & Objectives Overview This lesson provides an understanding of the communication exchange between an access point and a wireless controller in a Cisco Unified Wireless Network environment. Objectives - Upon completing this lesson, you will be able to describe the mechanism by which an access point associates to a wireless controller. This ability includes being able to meet these objectives: Define Ports, Interfaces, and WLANs Contrast these methods: Broadcast, DHCP option, and DNS option, of discovering a controller List the naming conventions for a primary controller List the steps needed to configure the AP for High Availability Describe how to configure a controller to be a master controller Describe AP Fallback Describe the appliance mode failover process Describe the appliance mode high availability N+1 design List the number of access points supported by each controller platform Describe the purpose and function of Aggressive Load Balancing 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-2
AP Controller Discovery Controller Discovery order: Layer 2 join procedure attempted on LWAPP APs (CAPWAP does not support layer 2 APs) Broadcast message sent looking for controller on local subnet Layer 3 join process on CAPWAP APs and on LWAPP APs after Layer 2 fails Previously learned or primed controllers Subnet broadcast DHCP option DNS lookup 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-3 AP Controller Discovery Broadcast DHCP Server DHCP Offer DHCP Request 1 Layer 3 CAPWAP Discovery Request Broadcast 2 3 Layer 3 CAPWAP Discovery Responses (1 per AP-Manager Interface) 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-4
AP Controller Discovery DHCP Option DHCP Server DHCP Offer DHCP Request 1 Layer 3 CAPWAP Discovery Request Broadcast 2 DHCP Offer Contains Option 43 for Controller 3 Layer 3 CAPWAP Discovery Responses (1 per AP-Manager Interface) 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-5 AP Controller Discovery DNS Option DNS Server DHCP Server CISCO-CAPWAP-CONTROLLER.localdomain 192.168.1.2 2 DHCP Request 1 DHCP Offer 192.168.1.2 3 4 DHCP Offer Contains DNS Server or Servers 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-6
Primary Controller Name Primary controller name configuration controls to which Cisco WLC an AP will associate. Controller name included in discovery requests sent by Cisco WLC. Can assign secondary and tertiary Cisco WLCs to control AP association in the event of a network failure. Requires unique controller name for each Cisco WLC. Cisco WLC default controller name derived from Controller MAC address. Only useful for appliance mode AP. Primary controller name configuration is kept in flash; configuration not lost if powered off. 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-7 Configuring AP High Availability 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-8
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. 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-9 AP Fallback If the AP is registered to its secondary or tertiary controller, the AP will return back to its primary controller upon hearing discovery requests from the primary controller. Enabled by default. 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-10
AP Failover Process X Normal State Failover State Fallback 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-11 Controller High Availability Design N+1 1. Calculate number of appliance mode APs. 2. Divide the number of APs by maximum APs supported by controllers. 3. Add an additional controller to support the APs in the event of a failure. 48 APs Number of appliance mode APs equals 48+36+12=96 Number of APs divided by maximum APs supported by controller in appliance mode plus 1 (N+1) equals 96 / 50 = 2 + 1 = 3 controllers 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-12
Controller High Availability Design N+1 (Cont.) 4. On single controller failure, all APs will fail over. 5. APs should be primed with secondary and tertiary controllers. X 48 APs Number of appliance mode APs equals 48+36+12=96 Number of APs divided by maximum APs supported by controller in appliance mode plus 1 equals (N+1) 96 / 50 = 2 + 1 = 3 controllers 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-13 Controller High Availability Design N+N 1. Calculate number of appliance mode APs 2. Divide the number of APs by maximum APs supported by Controllers 3. Double the Number of Controllers to support all the APs in the event of multiple Controller failure Number of appliance mode APs equals 36+36+12+12=96 Number of APs divided by maximum APs supported by controller in appliance mode doubled equals (N+N) 96 / 50 = 2 + 2 = 4 controllers 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-14
Controller High Availability Design N+N (Cont.) 4. Two Controllers fail, all APs can still register 5. Clients are only limitedly affected by the failure X X Number of appliance mode APs equals 36+36+12+12=96 Number of APs divided by maximum APs supported by controller in appliance mode Doubled (N+N) 96 / 50 = 2 + 2 = 4 controllers 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-15 Number of APs Support per Platform Model Maximum APs Cisco WiSM 300 5508 12/25/50/100/250/500 * 4404 100 # 4402 12/25/50 * # 3750G 25/50* 2106/2112/2125 6/12/25 Cisco WLCM 6, 8, 12 or 25 APs attempt to associate with a controller in the following order: Primary, secondary, tertiary, master, least-loaded. The least-loaded controller will be part of the Mobility Group. * Limit based on software license # No more than 48 APs will be allowed on one port when not using LAG on the 4400 Series. 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-16
Aggressive Load Balancing Determines load on APs (on a single controller) and attempts to move new clients to less loaded APs. Go to Wireless > Advanced > Load Balancing to enable. Client Window Size is how many more clients an AP can have before it is considered as loaded. 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-17 Summary Several access point controller discovery methods are used. One controller in each subnet can be assigned as the master controller. AP fallback is enabled by default. In case of a failure of a WLC, the APs will fall back to their primary controller once the controller is back online. Controller High Availability Design N+1 provides a backup controller for the APs in the event of a controller failure. Controller High Availability Design N+N provides a full complement of backup controllers for the APs in the event of a single or multiple controller failure. A specific number of APs are supported by each controller platform. Aggressive load balancing determines the load on APs and attempts to move new clients to less loaded APs. 2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-18
2010 Cisco Systems, Inc. All rights reserved. CUWN v7.0 3-19