Explanation
The snat-route-change option is enabled by default. This option enables FortiGate to re-evaluate the routing
table and select a new egress interface if the next hop IP address changes. This option only applies to sessions
in the dirty state. Sessions in the log state are not affected by routing changes.

ADVPN is a technology that allows dynamic creation of IPsec tunnels between branch sites without requiring pre-configured policies or keys. BGP is a routing protocol that can be used to exchange routes between ADVPN peers. IBGP is a type of BGP that runs between routers in the same autonomous system (AS), while EBGP is a type of BGP that runs between routers in different ASes. IBGP is preferred over EBGP for ADVPN, because IBGP preserves the next hop information of the routes, which is needed to establish the IPsec tunnels. EBGP changes the next hop information to the EBGP peer address, which may not be reachable by the ADVPN peers. Therefore, using IBGP for ADVPN avoids the need to configure additional static routes or redistribute routes between BGP and another routing protocol. References = ADVPN with BGP as the routing protocol, ADVPN, SD-WAN self-healing with BGP, Technical Tip: ADVPN with BGP as the routing protocol The statement that IBGP is preferred over EBGP for ADVPN because IBGP preserves next hop information (D) is true. In a typical ADVPN deployment, it's beneficial to maintain next hop information across the network to ensure proper routing and optimal path selection. References: This understanding comes from my knowledge of Fortinet's SD-WAN and ADVPN configurations, where BGP's behavior in terms of next hop preservation is a key consideration.

Study Guide 7.2, pages 103 - 104. Another comment said "because without using application Control on the firewall policy, SDWAN can't work" but there is a app control "default" defined on config.