In an ADVPN (Auto-Discovery VPN) network, a dynamic VPN tunnel is established on-demand between spokes to optimize traffic flow and reduce latency.
Process:
1. Traffic Initiation:
A client behind Spoke-1 sends traffic to a device behind Spoke-2.

The traffic initially flows through the hub, following the pre-established overlay tunnel.

2. Hub Detection:
The hub detects that Spoke-1 is communicating with Spoke-2 and determines that a direct shortcut tunnel between the spokes can optimize the connection.

3. Shortcut Offer:
The hub sends a "Shortcut Offer" message to Spoke-1, informing it that a direct dynamic tunnel to Spoke-
2 is possible.

4. Tunnel Establishment:
Spoke-1 and Spoke-2 then negotiate and establish a direct IPsec tunnel for communication.

When multiple remote sites connect to the same hub using overlapping subnets, FortiGate needs to determine which route should be used for traffic forwarding. The route-overlap setting in IPsec Phase 2 allows FortiGate to handle this scenario by deciding whether to keep the existing route (use-old) or replace it with a new route (use-new).
In an ECMP (Equal-Cost Multi-Path) routing setup, both routes should be retained and balanced, but FortiGate does not support ECMP directly over overlapping routes in IPsec Phase 2. Instead, an administrator must decide which connection takes precedence using route-overlap settings.

FortiGate, like other security appliances, cannot analyze encrypted HTTPS traffic unless it decrypts it first. If only certificate inspection is enabled, FortiGate can see the certificate details (such as the domain and issuer) but cannot inspect the actual web content.
To fully analyze the traffic and detect potential malware threats:
# Full SSL inspection (Deep Packet Inspection) must be enabled in the SSL/SSH Inspection Profile.
# This allows FortiGate to decrypt the HTTPS traffic, inspect the content, and then re-encrypt it before forwarding it to the user.
# Without full SSL inspection, threats embedded in encrypted traffic may go undetected.

In the given ADVPN (Auto-Discovery VPN) topology, BGP is being used to dynamically establish routes between spokes. The neighbor-range configuration is crucial for simplifying BGP peer setup by automatically assigning neighbors based on their IP range.
set neighbor-group advpn
# The neighbor-group parameter is used to apply pre-defined settings (such as AS number) to dynamically discovered BGP neighbors.
# The advpn neighbor-group is already defined in the configuration, and assigning it to the neighbor-range ensures consistent BGP settings for all spoke neighbors.
set prefix 172.16.1.0 255.255.255.0
# This command allows dynamic BGP peer discovery by defining a range of potential neighbor IPs (172.16.1.1 - 172.16.1.255).
# Since each spoke has a unique /32 IP within this subnet, this ensures that any spoke within the 172.16.1.0
/24 range can automatically establish a BGP session with the hub.

To minimize CPU and RAM usage while still enforcing security features like web filtering and application control, SSL certificate inspection mode is the best choice.
# SSL certificate inspection allows FortiGate to inspect only the SSL/TLS handshake, including the Server Name Indication (SNI) and certificate details, without decrypting the full encrypted payload.
# This enables features like web filtering and application control because FortiGate can determine the destination website or application based on SNI and certificate information.
# It significantly reduces system load compared to full SSL inspection, which requires full decryption and re-encryption of traffic.