Including EPG-2, EPG-3, and EPG-4 in the preferred group allows these EPGs to communicate with each other without requiring any contracts. This is because the preferred group feature in Cisco ACI allows EPGs within the same VRF to communicate by default. However, since the secure server in EPG-1 must provide services to EPG-2, a contract is required between EPG-1 and EPG-2 to facilitate this communication while maintaining the security and policies necessary for the server.
References := For more detailed information on configuring EPGs and contracts in Cisco ACI, you can refer to the Cisco Data Center Core Technologies (DCCOR) study materials and official Cisco documentation. These resources provide comprehensive guidance on the implementation and management of EPGs, contracts, and preferred groups within a Cisco ACI environment.