Users Guide

Feature Guidelines and Limitations
Note the following guidelines and limitations before enabling this feature in your high availability deployment:
l Only APs that support 802.11n and 802.11ac can support client state synchronization.
l The client state synchronization and standby controller over-subscription features are mutually
incompatible and cannot be enabled simultaneously. If your deployment uses the standby controller over-
subscription feature, the feature must be disabled before enabling state synchronization.
High Availability Inter-Controller Heartbeats
The high availability inter-controller heartbeat feature allows for faster AP failover from an active controller to a
standby controller, especially in situations where the active controller reboots or loses connectivity to the
network.
The inter-controller heartbeat feature works independently from the AP mechanism that sends heartbeats
from the AP to the controller. If enabled, the inter-controller heartbeat feature supersedes the AP's heartbeat
to its controller. As a result, if a standby controller detects missed inter-controller heartbeats from the active
controller, it triggers its standby APs to failover to the standby controller, even if those APshave not detected
any missed heartbeats between the APs and their active controller. Use this feature with caution in deployments
where the active and standby controllers are separated over high-latency WAN links.
When this feature is enabled, the standby controller starts sending regular heartbeats to an AP's active
controller as soon as the AP has an UP status on the standby controller. The standby controller initially flags
the active controller as unreachable, but changes its status to reachable as soon as the active controller
sends a heartbeat response. If the active controller later becomes unreachable for the number of heartbeats
defined by the heartbeat threshold (default of 5 missed heartbeats), the standby controller immediately
detects this error and informs the APs using the standby controller to failover from the active controller to the
standby controller. If, however, the standby controller never receives an initial heartbeat response from the
active controller, and therefore never marks the active controller as initially reachable, the standby controller
will not initiate a failover.
This feature is disabled by default. It can be used in conjunction with the high availability state synchronization
feature only in topologies that use a single active and standby controller, or a pair of dual-mode active
controllers that act as standby controllers for each other. High availability inter-controller heartbeats can be
enabled and configured in the high-availability group profile using the WebUI or Command-Line interface.
For more details on how to enable and configure inter-controller heartbeats, see Configuring High Availability
on page 622.
High Availability Extended Controller Capacity
The standby controller over-subscription feature allows a standby controller to support connections to
standby APs beyond the controller's original rated AP capacity. This feature is an enhancement to the high
availability feature introduced in ArubaOS 6.3.0.0, which requires the standby controller to have an AP capacity
equal to or greater than the total AP capacity of all the active controllers it supports.
The following section of this document gives and lists requirements and capacity limitations for this feature.
For more details on enabling the extended standby controller capacity, see Configuring High Availability on
page 622.
Starting with ArubaOS 6.4.0.0, W-7000 Series and W-7200 Seriescontrollers that acts as a standby controller
can oversubscribe to standby APs by up to four times that controller's rated AP capacity, as long as the tunnels
consumed by the standby APs do not exceed the maximum tunnel capacity for that standby controller.
Dell Networking W-Series ArubaOS 6.5.x | User Guide Increasing Network Uptime Through Redundancy and VRRP |
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