# Communication between Firewall Cluster nodes

Information between Firewall Clustered nodes is synchronized through selected interfaces via a heartbeat network that uses multicast transmissions.

The Firewall Cluster nodes exchange information constantly. The state tables that list open connections (state sync) and the operating state of the other nodes (heartbeat) are exchanged. This exchange of information guarantees that all nodes have the same information about the connections. If a firewall node becomes unavailable, the other nodes of the cluster immediately notice the change. The exchange of information between clustered Firewall nodes is synchronized through selected interfaces via a heartbeat network using multicast transmissions. The heartbeat messages are authenticated, and can also be encrypted if necessary. Authentication is enabled by default.