The customer needs a solution that can terminate VPN tunnels for Aruba RAPs, which are remote access points that connect to the corporate network over the Internet. The customer has only one public IP address, which means that they need to use NAT to forward the IPsec traffic to the device that will terminate the VPN tunnel. The customer also wants N+1 redundancy, which means that they need at least two devices that can act as backup for each other in case of failure.

The solution that meets the customer requirements is to use two Aruba MCs on the same subnet that use VRRP without clustering. VRRP stands for Virtual Router Redundancy Protocol, and it is a protocol that allows multiple devices to share a virtual IP address and act as a single gateway for the network. This way, the customer can use the virtual IP address as the public IP address for the NAT, and the IPsec traffic will be forwarded to the device that is the VRRP master. If the master device fails, the backup device will take over the role of the master and continue to terminate the VPN tunnels. This provides N+1 redundancy for the customer.

The other options are not suitable for the customer requirements:

Option B is not suitable because a Layer 3 cluster requires two public IP addresses, one for each MC. The customer only has one public IP address, so they cannot use this option.

Option C is not suitable because VRRP does not work across different subnets. The customer needs to have the MCs on the same subnet to use VRRP.

Option D is not suitable because a Layer 2 cluster does not support NAT. The customer needs to use NAT to forward the IPsec traffic to the MCs.

References:

Aruba Remote Access Point (RAP) Networks Validated Reference Design)

Aruba Mobility Controller Virtual IP Configuration Guide)

ArubaOS 8.5 User Guide)