Sure Pass Exam NSE8_812 PDF

A is correct because using network-overlay id allows you to configure multiple ADVPN tunnels on a single interface with a single IP address on the DC FortiGate. This is explained in the FortiGate Administration Guide under ADVPN > Configuring ADVPN > Configuring ADVPN on the hub. References:

Graceful-restart is a feature that allows BGP neighbors to maintain their routing information during a BGP restart or failover event, without disrupting traffic forwarding or causing route flaps. Graceful-restart works by allowing a BGP speaker (the restarting router) to notify its neighbors (the helper routers) that it is about to restart or failover, and request them to preserve their routing information and forwarding state for a certain period of time (the restart time). The helper routers then mark the routes learned from the restarting router as stale, but keep them in their routing table and continue forwarding traffic based on them until they receive an end-of-RIB marker from the restarting router or until the restart time expires. This way, graceful-restart can minimize traffic disruption and routing instability during a BGP restart or failover event. References: