User's Manual

573 | Increasing Network Uptime Through
Redundancy and VRRP
Dell Networking W-Series ArubaOS 6.4.x| User Guide
Figure 61 Redundancy with a Active-Backup Master Controller Pair
When a VRRP instance is configured on the controller vlan, there would be no change in the VRRP state if the failover
scenario is tested by shutting down the port or bringing down the vlan. The controller continues to remain 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, but 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 to the standby controller. If an AP fails to
connect to the first standby controller, the active controller will select a new standby controller for that AP, and
the AP will attempt 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 manually triggers a failover 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 you enable this
feature, clients only have 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. For the
procedure to enable the client state synchronization feature, see Configuring High Availability on page 576,