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

The correct design is to deploy the application in both data centers, advertise the application prefix from DC1 as a /32, and advertise a broader /24 from DC2. This uses longest-prefix-match behavior to create deterministic primary and backup routing. Cisco routing logic prefers the most specific matching route in the routing table, regardless of administrative distance or metric comparisons among less specific covering routes. As long as the DC1 /32 is present, traffic for that exact application address follows DC1. If DC1, its edge path, or the /32 advertisement fails, the /32 is withdrawn and the remaining /24 covering route from DC2 provides backup reachability. Advertising the same prefix from both locations may result in load sharing or provider-dependent selection, which does not guarantee DC1 primary behavior. IP SLA could be used in some route-tracking designs, but the clean routing solution tested here is prefix specificity. Reference topics: longest-prefix match, BGP advertisement, active/standby data center routing, covering routes, route failover.

Root guard is the correct feature when the design must allow switches to be attached for testing but prevent those switches from influencing the spanning-tree root placement. Cisco root guard protects the intended STP root by placing a port into a root-inconsistent state if superior BPDUs are received on a port where the root should never appear. This directly addresses the risk created by rogue or lab switches connected by end users: if a user switch advertises a better bridge priority, the production access topology is not allowed to reconverge around that unauthorized device. BPDU guard is usually used on PortFast edge ports to err-disable a port that receives any BPDU, which is excellent for strict host-only ports but less aligned with the wording that users may connect their own switches for testing. Loop guard protects root or alternate ports from losing BPDUs and accidentally forwarding. BPDU skew detection is a diagnostic feature, not the correct design control. Therefore, root guard is the appropriate protection against rogue switches affecting STP topology. Reference topics: STP root placement, root guard, superior BPDUs, campus Layer 2 protection.

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.