Alcatel-Lucent AOS-W 6.5.3.x - Configuring High Availability

638| Increasing Network Uptime Through Redundancy and VRRP AOS-W 6.5.3.x| User Guide
Feature Requirements
This feature can be enabled on switches in a master-local topology where centralized licensing is enabled on the
active and standby switches, or on independent master switches that are not using VRRP-based redundancy. If
centralized licensing is disabled, the standby AP over-subscription feature is also disabled. Standby switch over-
subscription and the high availability state synchronization features are mutually incompatible and cannot be
enabled simultaneously. If your deployment uses the state synchronization feature, you must disable it before
you enable standby switch over-subscription.
Standby Switch Capacity
The following table describes the AP over-subscription capacity maximum supported tunnels and the switches
that support this feature.
To determine the number of standby tunnels consumed by APs on each active switch, multiply the number of
APs on the active switches by the number of BSSIDs per AP. For example, consider a deployment with four
active OAW-4550switches that each have 512 APs with 8 BSSIDs. The APs on each active switch consume (512
* 8) tunnels, for a combined total of 16,384 tunnels. A single OAW-4550switch using the standby switch over-
subscription feature can act as the standby switch for all four active switches in this example because this
topology is within the 4x rated AP capacity limit and maximum tunnel limit for the OAW-4550switch model.
If the network administrator later changed all the APs in this deployment to support 10 BSSIDs, each active
switch would use (512 * 10) tunnels, for a combined total of 20,480 tunnels on the four active switches. The
tunnels required by the APs on the active switches would then exceed the maximum tunnel limit for the
standby switch, so the standby switch can no longer support all APs on the active switches. Dynamic changes
to configuration (such as the addition of BSSIDs to any AP group) causes all the standby APs to disconnect and
reconnect back to the standby switch defined by their updated configuration
To view information about the numbers of currently associated APs and supported BSS tunnels, and the
remaining capacity for additional APs and BSStunnels, issue the CLIcommand show ha oversubscription
statistics.
AP Failover
If a standby switch reaches its AP over-subscription capacity or exceeds its maximum BSSID limit, the standby
switch drops any subsequent standby AP connections. A dropped AP attempts to reconnect to the standby
switch, but after it exceeds the maximum number of request retries, the AP informs the active switch that it is
unable to connect to the standby switch. The active switch then prompts the APto create a standby tunnel to
another standby switch, if one is configured.
If an active switch fails, the APs on the active switch failover to the standby switch. Once the standby switch
has reached its capacity for active APs, it terminates tunnels to any standby APs that the switch can no longer
serve. When these APs detect that there is no longer a heartbeat between the AP and the standby switch, they
notify their active switch that they can no longer connect to the standby. The active switch then promptsthe
APs to establish standby tunnels to another standby switch, if one is configured.
Configuring High Availability
A switch using this feature can have one of three high availability roles: active, standby, or dual. An active
switch serves APs, but cannot act as a failover standby switch for any AP except those that it serves as an active
switch. A standby switch acts as a failover backup switch, but cannot be configured as the primary switch for
any AP. A dual switch can support both roles, acting as the active switch for one set of APs, and a standby
switch for another set of APs.
Starting with AOS-W 6.4, a switch is assigned the dual role if no other role is specified