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

DiffServ is the correct scalable QoS architecture for classifying traffic according to business requirements and using DSCP values as the priority descriptor. Cisco QoS design distinguishes DiffServ from IntServ. IntServ uses per-flow signaling with RSVP and can reserve resources, but that model is not operationally scalable across large enterprise networks. DiffServ is class-based. Traffic is classified and marked at the network edge, then each device applies per-hop behavior to those classes using local QoS policy. DSCP provides a six-bit field in the IP header, which supports more than ten classification values and allows standardized treatment classes such as EF, AF, class selector, and default. Best effort provides no differentiated treatment, and RSVP is a signaling mechanism associated with IntServ rather than the requested scalable class-based architecture. “Interserv” is not the correct Cisco QoS model term. Therefore, the engineer should design around DiffServ, with a clear trust boundary, marking policy, queuing model, and consistent treatment across WAN and campus boundaries. Reference topics: DiffServ, DSCP, per-hop behavior, class-based QoS, scalable QoS architecture.

For model-driven telemetry with periodic updates, the architect must understand that each periodic update sends the subscribed data at the configured interval. Cisco telemetry guidance distinguishes periodic subscriptions from on-change subscriptions. A periodic subscription streams a full copy of the subscribed data element or table at each interval, even if the underlying state has not changed. That behavior is useful when the collector needs regular time-series samples, trending, or baseline monitoring, but it creates predictable bandwidth and collector-load requirements. On-change subscriptions are different: they publish updates when the subscribed state changes and are more efficient for state changes such as interface status, memory thresholds, or protocol adjacency m ovement. Empty subscription behavior and initial update timing may matter in specific implementations, but they are not the main design consideration in this question. Since the customer requires periodic updates, the design must size the transport, collector, retention system, and subscription intervals around repeated full data delivery. Reference topics: model-driven telemetry, periodic subscription, on-change subscription, YANG-modeled operational data, collector sizing.

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.