Two-factor authentication is a security feature that requires users to provide two forms of information before gaining access to the Cisco ESA. The two factors are usually something the user knows, such as a password, and something the user has, such as a token or a code. Two-factor authentication can be enabled for specific user roles on the Cisco ESA through a RADIUS server, which is an external authentication server that supports the Remote Authentication Dial-In User Service (RADIUS) protocol. The RADIUS server can generate and validate the second factor for the users, such as a one-time password (OTP) or a time-based one-time password (TOTP). To enable two-factor authentication through a RADIUS server, the network engineer must configure the RADIUS server settings on the Cisco ESA, and assign the user roles that require two-factor authentication to use the RADIUS server as the authentication source. This can be done on the System Administration > Users page in the web interface, or by using the userconfig command in the CLI12.
A cluster is a group of Cisco ESAs that share the same configuration information and can be managed centrally. A cluster can provide increased reliability, flexibility, and scalability for the email security system. To join a cluster, a Cisco ESA must have the same AsyncOS version as the other cluster members, and must use a pre-shared key to authenticate with the cluster leader. The pre-shared key is a secret passphrase that is configured on the cluster leader and must be entered on the joining appliance. To join a cluster by using the Cisco ESA CLI, the network engineer must use the clusterconfig command, which allows the engineer to create a new cluster, join an existing cluster, or leave a cluster. The clusterconfig command also allows the engineer to specify the communication port and the hostname or IP address of the cluster leader. If the Cisco ESA has enabled two-factor authentication, the network engineer must also use the clusterconfig > prepjoin command to configure the pre-shared key before joining the cluster34.
Therefore, option A is the correct answer, and the other options are incorrect. Option B is incorrect because the cluster configuration options must be done via the CLI on the Cisco ESA and cannot be created or joined in the GUI. Option C is incorrect because the Cisco ESA does not support TACACS+ as an external authentication source, only LDAP and RADIUS. Option D is incorrect because it also uses TACACS+, which is not supported by the Cisco ESA. References :=
User Guide for AsyncOS 14.0 for Cisco Secure Email Gateway - GD (General Deployment) - Distributing Administrative Tasks
User Guide for AsyncOS 14.0 for Cisco Secure Email Gateway - GD (General Deployment) - External Authentication
Configure an Email Security Appliance (ESA) Cluster
User Guide for AsyncOS 14.0 for Cisco Secure Email Gateway - GD (General Deployment) - Centralized Management
