26-2Figure 26-1 Network diagram for a clusterAs shown in Figure 26-1, the device configured with a public IP address and performs themanagement function is the management device, the other managed devices are member devices,and the device that does not belong to any cluster but can be added to a cluster is a candidate device.The management device and the member devices form the cluster.Figure 26-2 Role change in a clusterAs shown in Figure 26-2, a device in a cluster changes its role according to the following rules:z A candidate device becomes a management device when you create a cluster on it. Amanagement device becomes a candidate device only after the cluster is removed.z A candidate device becomes a member device after being added to a cluster. A member devicebecomes a candidate device after it is removed from the cluster.How a Cluster WorksCluster management is implemented through HW Group Management Protocol version 2 (HGMPv2),which consists of the following three protocols:z Neighbor Discovery Protocol (NDP)z Neighbor Topology Discovery Protocol (NTDP)z ClusterA cluster configures and manages the devices in it through the above three protocols. Clustermanagement involves topology information collection and the establishment and maintenance of acluster. Topology information collection and cluster maintenance are independent from each other, withthe former starting before the cluster is created:z All devices use NDP to collect the information of the directly connected neighbors, including theirsoftware version, host name, MAC address and port number.z The management device uses NTDP to collect the information of the devices within user-specifiedhops and the topology information of all devices and specify the candidate devices of the cluster.z The management device adds or deletes a member device and modifies cluster managementconfiguration according to the candidate device information collected through NTDP.
