Cisco WLC High Availability Configurations

Fig 1: Cisco WLC HA Configurations

High Availability (HA) in Cisco Wireless LAN Controllers (WLCs) ensures continuous operation of wireless networks by providing redundancy. In an HA setup, one WLC functions as the Primary controller, while another serves as the Secondary (Standby) controller. The Secondary WLC seamlessly takes over in the event of a Primary WLC failure, ensuring uninterrupted service.

The provided commands configure WLCs in an HA setup using Stateful Switchover (SSO). Below is an explanation of the key concepts and commands:

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Primary Node Configuration:

1. Management IP:

   • 192.168.2.253
   • This is the primary WLC's management interface IP address, used for accessing and managing the controller.

2. Redundancy Management IP:

   • 192.168.2.251
   • This IP is used exclusively for HA communication between the Primary and Secondary WLCs.

3. Command: config redundancy unit primary

   • Configures the WLC as the Primary Unit in the HA pair. This unit actively handles traffic and manages access points (APs) during normal operation.

4. Command: config redundancy mode sso

   • Sets the HA mode to Stateful Switchover (SSO). In SSO:
     • Both controllers share the same configuration.
     • The Secondary WLC continuously syncs its state with the Primary.
     • In case of Primary WLC failure, the Secondary takes over with minimal disruption, as client and AP states are preserved.

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Secondary Node Configuration:

1. Management IP:

   • 192.168.2.254
   • The management interface IP address for the Secondary WLC, used for administrative purposes.

2. Redundancy Management IP:

   • 192.168.2.252
   • This IP is used for communication with the Primary WLC.

3. Command: config redundancy unit secondary

   • Configures the WLC as the Secondary Unit in the HA pair. This unit operates in a passive state during normal operation, ready to take over if the Primary fails.

4. Command: config redundancy mode sso

   • Similar to the Primary WLC, this configures the HA mode as SSO. The Secondary WLC remains in sync with the Primary, ensuring a seamless failover process.

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Additional Details on SSO Mode:

• Synchronization:
  • The configuration, AP database, and client information are replicated from the Primary to the Secondary.
• Failover Time:
  • The switchover is nearly instantaneous, typically within milliseconds, due to the constant synchronization.
• AP and Client Behavior:
  • Access Points do not reboot or rejoin during failover.
  • Client sessions are preserved, minimizing impact on users.

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Benefits of WLC HA with SSO:

1. High Availability: Ensures uninterrupted wireless services by providing redundancy.
2. Seamless Failover: Minimizes downtime during controller failures.
3. Centralized Management: Both controllers share a unified configuration, simplifying management.

This configuration is ideal for environments that require continuous wireless availability and minimal downtime.