The branch-to-branch topology in Azure Virtual WAN is characterized by direct connectivity between branches through the Virtual WAN backbone, which reduces dependency on centralized hubs. This results in a simplified network architecture, lowering latency and optimizing routing between branch locations.

The route server subnet in Azure is a dedicated subnet that hosts the Azure Route Server, which functions as the hub for dynamic routing information exchange between Azure virtual networks and BGP-enabled network virtual appliances (NVAs) or on-premises routers. It enables seamless and centralized route propagation.

The FortiGate VM and the Windows Server VM are in different subnets but within the same Production virtual network, which means they can communicate by default unless restricted. Azure allows ICMP between subnets, but Windows VMs have ICMP blocked by default in their firewall settings. Therefore, the likely reason for the ping failure is that the Windows Server’s firewall is blocking ICMP (ping) traffic.