WESM zl Management and Configuration Guide WT.01.28 and greater

10-7
Redundancy Groups
High Availability for Wireless Services
■ one Wireless Edge Services zl Module with the default license (for 12 RPs)
■ one Redundant Wireless Services zl Module
The redundancy group has two licenses and can adopt 24 RPs.
All members of the redundancy group share the group’s licenses. Any active member
can use the groups’ licenses to adopt an RP at any time. Any standby member can
use the groups’ licenses to adopt an RP in the circumstances listed in “Adopting RPs
in Standby Mode” on page 10-6.
Establishing a Redundancy Group
To ensure that each module recognizes that it is part of a redundancy group and knows
the IP address of the other modules in the group, you must complete the steps to
configure a redundancy group on each module. In addition, you must ensure that the
modules can communicate with one another. For example, if the modules are installed
in different wireless services-enabled switches, the switches must be connected either
directly or indirectly (through one or more infrastructure switches).
When you configure and enable a redundancy group on a module, that module begins
the process of establishing a group. To successfully complete this process, the module
must receive communications from the other modules in the redundancy group.
The process for establishing a redundancy group is the same for both primary and
redundant modules. If all modules all configured correctly as a redundancy group,
each will go through the following stages in establishing a group:
■ Startup state—The redundancy service starts on the module.
■ Discovery state—The module begins to send heartbeat messages to advertise
that it is available. It listens for the other modules to send heartbeat messages to
verify that its peers are also available.
In addition, the module sends an update message, listing the current values for
its redundancy group settings, such as heartbeat time, discovery time, hold time,
redundancy ID, and redundancy protocol version. The other modules send an
update message as well. The modules compare their redundancy group settings
to ensure that they are the same. If the modules are not using the same settings,
they cannot establish a functioning redundancy group.
■ Online state—If the modules can reach each other and they are using the same
redundancy group settings, they change their status to online. In this state, a
standby module can take over for an active module if the active module becomes
unavailable. However, you must configure the standby modules to provide
wireless services, as explained in “Creating Matching Configurations for the
Redundancy Group” on page 10-8.