Replication communicates using a proprietary binary protocol that is implemented on top of the TCP/IP protocol using SSL encryption. Some protocol messages are used for administrative purposes (such as WAN Gateway server negotiation or flow control), some carry updates to replicated data, while others are directed to all servers for monitoring requests.
In a replicated topology, each participating Directory Server is connected to every other server via the replication server port in order to monitor health. Servers which share the same location setting are also connected to rapidly replicate changes and lastly the WAN Gateway servers are all interconnected to replicate changes across locations.
Directory Servers keep connections open as long as possible to reduce the communication latency when messages are exchanged. Heartbeat messages are transmitted on a regular basis to detect a network failure or an unresponsive directory server as early as possible. Heartbeat messages also prevent idle connections from being closed by firewalls.
The following detailed communication flow will be used to describe major components of replication. This illustration is the expanded view of figure shown in the Overview section.