300-420 Exam Dumps : Designing Cisco Enterprise Networks (ENSLD) v1.1

DMVPN Phase 3 hub-and-spoke is the best design for this requirement. The customer wants secure dynamic site-to-site VPN connectivity for voice, video, and FTP, and also wants branches to communicate directly instead of hairpinning all traffic through headquarters. DMVPN supports dynamic spoke-to-spoke tunnels using multipoint GRE, NHRP, and IPsec protection. Phase 3 is more scalable than Phase 2 because the hub can send NHRP redirect messages and spokes can install shortcut routes, reducing the need for every spoke to maintain detailed next-hop information for every other spoke. That is important because the branch routers have limited memory. Phase 1 is hub-and-spoke only and does not provide dynamic spoke-to-spoke forwarding. A hierarchical Phase 3 design can be useful at very large scale, but the question describes a headquarters and remote branch design rather than multiple tiers of hubs. Phase 3 hub-and-spoke satisfies direct branch communication, security, and scale. Reference topics: DMVPN Phase 3, NHRP redirect, spoke-to-spoke tunnels, IPsec encryption, branch WAN scalability.

BFD is not required for the specific failure described: a physical fiber break on point-to-point routed links. In a Layer 3 campus or routed-access design, a direct physical link failure is detected by the interface state change, so the routing protocol can react immediately without waiting for hello/dead timers. Cisco campus design guidance favors point-to-point routed links partly because they give rapid convergence and avoid STP delays. BFD is valuable when a forwarding-path failure is not reliably detected by Layer 1 or Layer 2, or when a protocol adjacency must detect loss faster than its native timers. It does not automatically create convergence by itself; it detects failure and notifies the routing protocol. For a clean fiber cut on a routed point-to-point link, link-down detection is already fast enough for sub-second failover in the design. OSPF timer tuning is also not the preferred design answer for this physical-failure case. Reference topics: routed access design, point-to-point links, link-failure detection, BFD, OSPF convergence.

Explicit QoS trust should be configured at the network boundary points where markings first enter the managed DiffServ domain and are known to be reliable. In a DiffServ design, traffic classification and marking are typically performed at the access edge or at a controlled ingress boundary, and downstream devices then honor DSCP or CoS markings based on the trust boundary. Cisco QoS design stresses that the trust boundary must be intentionally placed; endpoints or unmanaged devices should not be trusted by default because they can mark traffic incorrectly and steal priority treatment. The exhibit answer identifies B and E as the correct trust points, meaning those are the controlled ingress locations where markings should be accepted. Options that trust uncontrolled endpoint-facing points or internal transit locations would either create a security problem or add no practical value. Once traffic is trusted and marked at the correct boundary, queuing, policing, and shaping policies can use the DSCP values consistently across the campus or WAN. Reference topics: DiffServ, QoS trust boundary, DSCP marking, classification, enterprise QoS design.