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

BFD is the correct design feature for detecting a link failure within 200 ms or less without materially increasing OSPF control-plane load. Cisco uses Bidirectional Forwarding Detection as a fast, lightweight failure-detection protocol that can be associated with routing protocols such as OSPF. Instead of relying on aggressive OSPF hello and dead timers, BFD performs rapid forwarding-path checks and notifies OSPF when the path fails. This allows fast convergence while avoiding the additional routing-protocol overhead and instability that can come from very low hello timers. UDLD detects unidirectional Layer 2 fiber failures, but it is not the routing adjacency failure-detection mechanism requested here. Carrier delay can adjust interface state transition timing, but it does not provide a routing-protocol independent liveness session. Fast hellos can reduce detection time, but they increase protocol traffic and can affect overall performance. BFD is therefore the proper design choice for fast and efficient OSPF convergence. Reference topics: BFD, OSPF convergence, fast failure detection, routed campus resiliency, control-plane efficiency.

The multicast-replicator function is used to optimize multicast traffic distribution across Cisco SD-WAN. Cisco Catalyst SD-WAN multicast overlay design avoids forcing the ingress WAN Edge router to replicate every multicast packet to every remote receiver. Instead, multicast routes and receiver information are exchanged through OMP, and a WAN Edge can be designated as a multicast or OMP replicator. The replicator then distributes streams to interested receivers across the overlay, reducing bandwidth and processing pressure on the source-side edge. That is why multicast-replicator is the feature that optimizes WAN bandwidth for IGMP-driven multicast receiver traffic among WAN Edge routers in the same VPN. IGMPv2 is only the host-to-router group membership protocol and does not optimize overlay distribution by itself. A multicast RP is used in PIM sparse mode, but it is not the SD-WAN overlay replication feature. Multicast service routes advertise multicast service information, but the bandwidth-saving forwarding role is the replicator. Reference topics: Cisco SD-WAN multicast overlay, OMP multicast routes, multicast replicator, IGMP receiver joins.

The Cisco SD-Access component mapping is based on the normal fabric roles. A fabric edge node is the access-facing fabric device that connects wired endpoints and fabric access points, acts as the anycast Layer 3 gateway, encapsulates endpoint traffic into VXLAN, and registers endpoint reachability with the control plane. A control-plane node supplies the LISP map-server and map-resolver functions, maintaining endpoint-to-location mappings. A border node connects the fabric to external Layer 3 domains, shared services, WAN, Internet, or another fabric/transit domain, and it de-encapsulates traffic as it leaves the fabric. Intermediate nodes provide routed IP transport inside the underlay and move packets between edge, border, and control-plane nodes without owning endpoint policy or registration. This role separation is important because a design failure often comes from assigning the wrong function to the wrong node. Access-facing policy and endpoint onboarding belong at the edge; external connectivity belongs at the border; location resolution belongs to the control plane; transport belongs to intermediate nodes. Reference topics: SD-Access fabric roles, edge node, border node, control-plane node, intermediate node.