Creating a physical standby database using RMAN active database duplication requires certain prerequisites to ensure a successful and seamless operation:
Configure Oracle Net connectivity on the primary host to the standby database instance (A): Proper Oracle Net connectivity between the primary and standby servers is essential for communication and data transfer during the duplication process. Oracle Net services provide the network foundation for Oracle Database, Oracle Net Listener, and Oracle applications.
Establish user equivalence for the database software owner between the primary host and standby host (B): User equivalence ensures that the user who owns the Oracle Database software on the primary server has the same privileges on the standby server. This is crucial for RMAN to perform operations on both servers without encountering permission issues.
Startup nomount the standby database instance (C): The standby database instance needs to be started in the NOMOUNT stage before the duplication can begin. This prepares the environment for creating the control file and restoring the database without mounting it, which is a necessary step in the RMAN duplication process.
Reference:
Oracle Database Backup and Recovery User's Guide
Oracle Data Guard Concepts and Administration

* DB_NAME (A): The name of the database, which should remain consistent across the primary and standby databases.
* db_file_name_convert (C): This parameter helps define the mapping of data file names from the primary to the standby database, which is crucial during the creation and operation of a standby database.
* COMPATIBLE (D): The compatibility level can influence the features that can be used on the standby database and must be consistent with or higher than that of the primary database, especially after upgrades.
* STANDBY_ARCHIVE_DEST (F): This parameter specifies the destination of archived redo log files on the standby database, which is important for log transport and apply services.
References:
* Oracle Data Guard Concepts and Administration Guide
* Oracle Database Reference

Far Sync instances are a feature of Oracle Data Guard designed to support zero data loss protection over long distances:
* The Data Guard Broker must be used to deploy and manage Far Sync instances (A): Data Guard Broker simplifies the deployment and management of Far Sync instances, which are an integral part of zero data loss protection configurations.
* They enable standby databases to be configured at remote distances from the primary without impacting performance on the primary (C): Far Sync instances are designed to receive redo from the primary database and then forward it to a remote standby database, thereby avoiding any performance
* impact on the primary database itself.
* A primary database can ship redo directly to multiple Far Sync instances (E): A primary database can be configured to send redo logs to more than one Far Sync instance, which can then forward the redo to their respective remote standby databases.References:
* Oracle Data Guard Concepts and Administration Guide
* Oracle Database High Availability Overview

When issuing a "switchover to sheep;" command in a Data Guard configuration, the primary database (Dogs) transitions to a standby role, and the target standby database (Sheep) becomes the new primary database.
Fast-Start Failover (FSFO) remains enabled, but its target changes according to the new roles of the databases.
Since Cats is also a physical standby database, it does not become the failover target by default unless it is specified in the broker configuration. After the switchover, the original primary (Dogs) becomes the new standby database and thus the new failover target for FSFO.References:Oracle Data Guard Broker documentation provides detailed procedures and explanations of switchover operations, including how FSFO targets are affected post-switchover. This behavior is consistent across different Oracle Database versions that support Data Guard and FSFO.