Extreme Networks Summit WM3000 Series Reference Manual page 271

After sending the command to other members, the cluster-management protocol (at WS1) waits for a
response from the members of the redundancy group. Upon receiving a response from each member,
WS1 updates the user's screen and allows the user to enter/execute the next command.
The wait time required to collect responses from other controllers is predefined, so if any one or more
members does not respond to a given command within the defined interval, the command originating
controller displays whatever responses have been collected and ignores the delayed responses. This
time-based response mechanism eliminates the possibility of indefinite response hangs and allows for
quicker redundancy group configuration.
There is no fixed master-slave relationship between members. Typically, a controller can be considered a
master for the command it originates. Responding members can be considered slaves with respect to
that command.
This virtual master-slave relationship makes this design unique when compared to existing centralized
management systems. Having a virtual master-slave relationship eliminates a single point of failure,
since a user can make use of any controller as the group centralized management entity (using the
cluster-management context).
NOTE
When using the redundancy feature make sure that UDP traffic on port 51515 is open between the redundant
controllers.
Summit WM3000 Series Controller System Reference Guide
271