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.