Using FortiGate at both ends of a site-to-site IPsec VPN tunnel provides the advantage of applying consistent security policies, configurations, and management tools across both the on-premises and Azure environments. This simplifies policy enforcement, improves operational efficiency, and ensures uniform threat protection.

A user-defined route (UDR) in Azure is used to redirect traffic from other VMs through a FortiGate VM for inspection. By modifying the routing table, you ensure that outbound or inter-subnet traffic is sent to the FortiGate as the next hop, enabling traffic filtering, logging, and security enforcement.