Elasticsearch operates using a full mesh network topology, where each node in a cluster maintains a connection to every other node, simplifying code by using one-way connections. When a node starts, it uses unicast and multicast messages to discover and connect with other nodes in the cluster, allowing it to quickly integrate. Both client nodes, which fully participate in the mesh, and transport clients, which do not require back connections, are supported. Communication between nodes primarily relies on TCP connections, which Elasticsearch organizes into channels to separate different types of traffic, such as recovery, bulk operations, regular operations, state changes, and pings for fault detection. Each new instance added to a cluster establishes multiple connections with each node, and the linked nature of these channels can make the system vulnerable to network issues, discouraging the creation of clusters across distant data centers.