SRX chassis clustering is a high availability feature that allows two SRX Series devices to operate as a single logical device. The two devices are connected by a control link and a fabric link, which are used to synchronize the configuration, state, and traffic between the nodes. The control plane is responsible for managing the cluster configuration, monitoring the health and status of the nodes, and performing failover operations. The data plane is responsible for processing and forwarding the traffic through the cluster. SRX chassis clustering supports two modes for the data plane: active/passive and active/active. In active/passive mode, only one node is active for each redundancy group, which is a logical grouping of interfaces and services. The active node handles all the traffic for the redundancy group, while the passive node acts as a backup. In active/active mode, both nodes are active for different redundancy groups, and they can share the traffic load for the cluster. SRX chassis clustering supports only one mode for the control plane: active/passive. In this mode, only one node is the primary node, which is the master of the cluster configuration and the source of truth for the cluster state. The primary node also initiates the failover process in case of a node or interface failure. The other node is the secondary node, which is the slave of the cluster configuration and the backup of the cluster state. The secondary node takes over the primary role if the primary node fails or is manually disabled. References: Chassis Cluster Overview, SRX Series Chassis Cluster Configuration Overview, Chassis Cluster Overview