300-420 Exam Dumps : Designing Cisco Enterprise Networks

Nonstop Routing is the correct solution when the upstream router does not understand graceful restart messaging. Cisco NSF and graceful restart depend on helper behavior from neighboring routers. During a supervisor switchover, the restarting device asks neighbors to preserve forwarding and adjacency state while the control plane recovers. If the neighbor does not support or understand the graceful restart signaling, NSF cannot deliver the intended benefit and route recomputation may still occur. NSR is different because it synchronizes routing protocol state between the active and standby supervisor internally, allowing the switch to preserve routing operation during stateful switchover without requiring graceful restart support from the neighbor. Remote LFA FRR protects against data-plane failures by precomputing repair paths, but it does not address supervisor switchover route recomputation. Aggressive IS-IS timers may make failure detection faster, but they increase control-plane churn and do not solve the lack of graceful-restart helper support. Therefore, the Catalyst switch should use NSR for this design. Reference topics: IS-IS high availability, NSR, NSF, graceful restart helper support, stateful switchover.

Cisco SD-Access uses virtual networks as macro-segmentation boundaries, and those VNs are represented as VRF instances in the fabric. By design, separate VNs do not communicate directly inside the overlay unless the design introduces controlled inter-VN routing. Cisco SD-Access designs commonly use an external fusion router, firewall, or shared-services device to map fabric VNs to external VRFs and selectively exchange routes between them. That is the correct design because it preserves segmentation while allowing policy-controlled access to shared resources or selected networks. GRE tunnels between fabric edges are not the normal SD-Access inter-VN communication method and would bypass the intended fabric policy model. Security Group Tags provide microsegmentation within or across policy domains, but SGTs do not by themselves leak routes between separate virtual networks. Route leaking on fabric border nodes is not the recommended standalone answer here because inter-VN communication is normally provided through a fusion device or firewall outside the fabric. Therefore, the correct solution is external fusion routing with controlled VRF route exchange.

BGP outbound route filtering is the correct solution because the enterprise wants control over which routes it receives without waiting for a provider change cycle each time the prefix set changes. Cisco BGP prefix-based ORF allows a receiving BGP speaker to send an inbound prefix-list filter to the remote peer, which then applies that list as an outbound filter. This reduces unwanted routing updates before they cross the session and lets the enterprise update the desired prefixes locally when business requirements change. Requesting only fixed prefixes from the ISP would work initially but fails the flexibility requirement because the provider has a two-week change process. Requesting a full table and filtering inbound would provide flexibility but wastes memory and CPU on the customer router because all routes are still received before filtering. A maximum-prefix limit does not select the correct routes. ORF is therefore the scalable operational design for receiving a default route and selected prefixes with minimal provider involvement. Reference topics: BGP ORF, prefix-based filtering, inbound route control, ISP peering design, routing table scale.