An LTM device has a virtual server mapped to www.

Comprehensive and Detailed Explanation From BIG-IP Administration Control Plane Administration documents: The Control Plane is responsible for ARP (Address Resolution Protocol) management for Virtual Addresses. For a Virtual Server to be reachable, the BIG-IP must respond to ARP requests for that IP. If the "ARP" setting is disabled on the Virtual Address properties, upstream routers cannot resolve the MAC address of the BIG-IP, leading to connectivity failure even if the service itself is "Available."