Replication servers are responsible for the following tasks:
Managing connections from directory servers
Connecting to other replication servers
Listening for connections from other replication servers
Receiving changes from directory servers
Forwarding changes to directory servers and to other replication servers
Saving changes to stable storage, which includes trimming older operations
Each replication server contains a list of all the other replication servers in the replication topology. Replication servers are also responsible for providing other servers with information about the replication topology. Even the smallest deployment must include two replication server instances, to ensure availability in case one of the replication server instances fails. There is usually no need for additional replication server instances unless the directory service must be able to survive more than one failure at a time, or unless the number of directory server instances must be very large.
Although replication servers do not store directory data, they are always LDAP servers or JMX servers. Like directory servers, replication servers can be configured, monitored, backed up and restored.