300-420 Exam Dumps : Designing Cisco Enterprise Networks

Running BFD between EIGRP neighbors is the appropriate design when the problem is traffic loss during link failure and the requirement is to reduce the impact of the failure. EIGRP can detect neighbor loss through its hello and hold timers, but those timers may not be fast enough for applications sensitive to packet loss. Bidirectional Forwarding Detection provides rapid failure detection independent of the routing protocol’s normal timer expiration. When BFD detects a failed forwarding path, it notifies EIGRP so the routing process can converge without waiting for the EIGRP hold timer. Summarization is still a valuable scaling technique, but it primarily reduces route table size and query scope; it does not directly accelerate failure detection on an individual inter-router link. Reducing EIGRP hello and hold timers can improve detection, but it increases control-plane load and is less efficient than BFD. The question emphasizes data loss when any one link fails, so fast failure detection is the best corrective design. Reference topics: EIGRP convergence, BFD, failure detection, hello and hold timers, routed-link resiliency.

The multicast Reverse Path Forwarding check is a loop-prevention mechanism. Cisco multicast forwarding does not forward traffic merely because the packet arrived on any multicast-enabled interface. Instead, the router checks whether the packet arrived on the interface that would be used to route traffic back toward the multicast source or, in shared-tree cases, back toward the rendezvous point. If the packet arrives on the expected reverse path, it passes the RPF check and can be replicated to the outgoing interface list. If it arrives on the wrong interface, it is dropped to prevent loops and duplicate packets. This supports a loop-free multicast distribution tree from sources to receivers. Auto-RP mapping agents, bootstrap messages, and RP-set discovery are separate rendezvous point distribution mechanisms; they are not the function of the RPF check. In enterprise designs with redundant links, asymmetric routing, or multiple equal paths, multicast RPF behavior must be reviewed carefully because unicast routing choices directly influence whether multicast packets are accepted or discarded. Reference topics: multicast RPF, PIM forwarding, loop prevention, outgoing interface list.

The SD-Access overlay should reduce subnet sprawl and avoid overlapping IP subnets unless there is a specific operational requirement. Cisco SD-Access creates overlay virtual networks over an IP underlay and uses anycast gateway, VXLAN encapsulation, LISP control-plane mapping, and policy constructs to simplify endpoint mobility and segmentation. Reducing the number of subnets simplifies DHCP scope management, default-gateway placement, and operational troubleshooting. Avoiding overlapping address space across overlay networks is also a practical design recommendation because overlapping subnets complicate shared services, fusion routing, security logging, and policy troubleshooting. LAN automation and a dedicated IGP process are underlay deployment considerations, not overlay design choices. Layer 3 to the access design is also associated with routed underlay and campus fabric transport, not the overlay segmentation model. A clean overlay design should define virtual networks, scalable groups, IP pools, shared-services reachability, and external connectivity before deployment. Reference topics: Cisco SD-Access overlay design, anycast gateway, virtual networks, DHCP simplification, overlapping subnet avoidance.