According to the Aruba Validated Design: Campus Wireless LAN1, MCs that are in different subnets cannot form a cluster, which is a logical group of MCs that share the same configuration and provide redundancy and load balancing for each other. However, MCs that are in different subnets can still provide backup LMS (local mobility switch) functionality for each other's APs. This means that if the primary MC that controls an AP fails, the AP can fail over to the backup MC that is in a different subnet. However, this failover is not stateful, meaning that the user sessions and firewall states are not preserved. Therefore, option D is the correct answer.
Option A is incorrect because the MCs can provide some level of redundancy for each other without being in the same subnet, as explained above. Option B is incorrect because VRRP is not required to provide redundancy for MCs that are in different subnets. VRRP is a protocol that provides redundancy for routers by creating a virtual router with a shared IP address. However, MCs do not act as routers, and they do not need a shared IP address to provide backup LMS functionality. Option C is incorrect because the MCs cannot be in a cluster if they are in different subnets, as explained above. Therefore, the cluster will not support any features, such as stateful failover, load balancing, or centralized configuration. References: Aruba Validated Design:
Campus Wireless LAN)