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

Route summarization should be planned from the aggregation layer toward both the core and the access layer. In hierarchical campus routing, aggregation or distribution devices are natural summarization boundaries because they sit between more specific access-layer networks and the core. Summarizing from aggregation toward the core prevents access-layer subnet churn from forcing unnecessary recomputation and route table growth in the core. Summarizing from aggregation toward access can also provide a concise upstream route, often a default or summary route, so access devices do not need the entire network routing table. The goal is to contain failures, reduce routing state, and preserve fast convergence at hierarchy boundaries. Summarizing from the core toward aggregation may hide useful topology details in the wrong direction, while summarizing directly from access toward aggregation is not always possible or efficient when access devices are numerous and have limited resources. The answer that places summarization at aggregation in both directions best matches Cisco hierarchical design principles. Reference topics: hierarchical campus design, route summarization, aggregation layer, core route scale, convergence containment.

The company must configure a summary route on R1. The branch routers must remain normal EIGRP routers, and auto-summary is not allowed, so the scalable design choice is manual summarization at the hub. Cisco EIGRP documentation states that manual summarization can be configured on an interface using the ip summary-address eigrp command and can summarize routes on almost any bit boundary. In a DMVPN hub-and-spoke topology, a hub summary reduces the number of individual routes advertised to branches, limits routing-table growth, and helps contain EIGRP queries. It also keeps branch configuration simple because the branches do not need to be converted to stub routers to meet this specific requirement. Disabling split horizon is a common DMVPN Phase 2 consideration when the hub must advertise spoke routes back out the same multipoint tunnel interface, but it does not summarize HQ routes. A multipoint interface is already implied by DMVPN, and disabling the SIA timer is not a design solution. Reference topics: EIGRP manual summarization, DMVPN hub design, no auto-summary, query containment.

Traffic shaping is required in the parent policy when hierarchical QoS uses CBWFQ in the child policy for low-bandwidth remote sites. In Cisco hierarchical QoS, the parent policy commonly shapes outbound traffic to the real available rate of the WAN service, especially when the physical interface speed is higher than the provider committed rate. The child policy then applies class-based queuing, such as CBWFQ and LLQ, inside the shaped rate. This structure creates an artificial congestion point on the router so the child queues can schedule packets predictably instead of allowing the provider to drop traffic after it exceeds the service rate. Policing in the child policy would drop excess packets and is not the normal prerequisite for nested CBWFQ. CBWFQ is supported in child policies within hierarchical designs, and parent shaping is the mechanism that makes the hierarchy effective. This is especially important on low-bandwidth WAN links where voice, video, and business-critical applications require deterministic treatment. Reference topics: hierarchical QoS, CBWFQ, parent shaping, child queuing, WAN QoS design.