Which command is used to set the CCP protocol to Multicast?

The command to set the CCP (Cluster Control Protocol) to Multicast is indeed found in the context of managing cluster configurations. The correct choice emphasizes the appropriate utility for cluster management, which is cphaconf.

Using cphaconf set_ccp multicast allows an administrator to configure the cluster to utilize Multicast for its CCP communications. This configuration is essential in environments where efficient data transfer and network resource optimization are priorities, as Multicast reduces the overhead on the network compared to other communication methods, such as Unicast.

When configuring cluster settings, it's crucial to select the right command depending on the context. The cphaprob command is primarily used for checking cluster status and operational states rather than setting configurations. Therefore, while it's involved in cluster management, it does not serve the purpose of establishing the CCP protocol mode. The focus on the cphaconf command makes choice B the appropriate answer when aiming to set the CCP to Multicast.