Wireless/Redundant Edge Services xl Module Management and Configuration Guide WS.01.03 or greater

4-4
Redundancy Groups
High Availability for Wireless Services
To ensure that each module recognizes that it is part of a redundancy group
and knows the IP address of the other module 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 exam-
ple, if the two modules are installed in different wireless services-enabled
switches, the two switches must be connected either directly or indirectly
(through one or more infrastructure switches).
Establishing a Redundancy Group
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 module in
the redundancy group.
If both the primary module and the redundant module are configured correctly
as a redundancy group, they will go through the following stages in establish-
ing a group. (The process for establishing a redundancy group is the same for
both the primary module and the redundant module. See Figure 4-2.)
■ 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 module to send a
heartbeat message to verify that its peer is 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 module sends an update message as well. The two
modules compare their redundancy group settings to ensure that they are
the same. If the two modules are not using the same settings, they cannot
establish a functioning redundancy group.
■ Online state—If the two modules can reach each other and they are using
the same redundancy group settings, they change their status to online.
In this state, the redundant module can take over for the primary module
if it becomes unavailable. However, you must configure the redundant
module to provide wireless services, as explained in “Configuring Wire-
less Services on the Redundant Wireless Services xl Module” on page
4-11.
If redundancy is not enabled for a module, it is in the disabled state.