Users Guide

620| Increasing Network Uptime Through Redundancy and VRRP Dell Networking W-Series ArubaOS 6.5.x| User Guide
Figure 79 Redundancy with a Active-Backup Master Controller Pair
When a VRRP instance is configured on the controller vlan, there is no change in the VRRP state if the failover
scenario was tested by shutting down the port or bringing down the vlan. The controller remains in the Master state
and sends VRRP advertisements, which do not reach the peer controller. When the port is down, the peer controller
becomes the Master. However, when the port on the previous master is enabled, it takes over the Master state. The
peer controller moves out of the master state when the original master sends a higher priority advertisement, even
when preemption is not enabled. The peer controller will not be preempted if the master controller crashes or
reboots.
AP Communication with Controllers
The High Availability features work across Layer-3 networks, so there is no need for a direct Layer-2 connection
between controllers in a high availability group.
When the AP first connects to its active controller, the active controller provides the IP address of a standby
controller, and the AP attempts to establish a tunnel to the standby controller. If an AP fails to connect to the
first standby controller, the active controller selects a new standby controller for that AP, and the AP attempts
to connect to that standby controller.
An AP will failover to its backup controller if it fails to contact its active controller through regular heartbeats
and keepalive messages, or if the user triggers a failover manually using the WebUI or CLI.
High Availability for bridge mode is supported on Campus APs. In this mode, the controller sends ACL Names
to the APs instead of the ACL IDs. These APs generate and maintain the mapping between the ACL Name and
ACL Id. In the event of a failover the ACL Name is sent to the AP from the stand-by controller. Since AP
maintains the mapping, the ACL Ids remain intact during a failover.
Client State Synchronization
Client state synchronization allows faster client reauthentication in the event of a controller failure by
synchronizing PMK and Key cache entries between active and standby controllers. When this feature is
enabled, clients only need to perform a four-way key exchange to reconnect to the network (instead of
performing a full authentication to the RADIUS server), dramatically shortening the time required for the client
to reconnect.
The following section of this document describes topologies, guidelines, and limitations for this feature. To view the
procedure for enabling the client state synchronization feature, see Configuring High Availability.