WESM zl Management and Configuration Guide WT.01.28 and greater

10-5
Redundancy Groups
High Availability for Wireless Services
■ Standby mode—In standby mode, the module is primarily responsible for
providing failover capabilities if a module in active mode becomes unavailable.
(A module in standby mode can adopt RPs in the circumstances described in
“Adopting RPs” on page 10-5.)
Both Wireless Edge Services zl Modules and Redundant Wireless Services zl
Modules support both modes. This difference between primary and redundant
modules lies in the redundant module’s lack of RP licenses, not in the modes in which
the modules function. For example, in a group that includes one primary module and
two redundant modules, you can configure the primary module in active mode and
the redundant modules in standby mode. But you can also choose to configure all
three modules in active mode. In fact, this is often a good idea because the active
modules load balance RPs between them, adding capacity to the network.
Note Selecting active mode for more than one module in a redundancy group still provides
high availability. If one module fails, another active module will adopt the failed
module’s radio ports.
Adopting RPs
How a Wireless Edge Services zl Module or Redundant Wireless Services zl Module
adopts RPs depends on the module’s mode.
Adopting RPs in Active Mode
All active members of a redundancy group can adopt RPs. By default, the modules
load balance the available RPs based on each module’s load value. When an RP is
detected, the active module with the lowest load value adopts that RP. If more than
one module has the same load value, the module with the lowest media access control
(MAC) address adopts the RP. The load value is based on the number of RPs adopted
by the module, not on the amount of traffic the RPs support.
Basing adoption on the load value is not always the best way to manage RPs, however.
Sometimes, you may want manual control over which RPs are adopted by which
module. See “Setting up Adoption Preference IDs to Control RP Adoption” on page
10-23 to learn how to use adoption preference IDs to determine which RPs each
module adopts.