300-420 Exam Dumps : Designing Cisco Enterprise Networks

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.

Dual stack is the correct migration strategy when the application chooses IPv6 or IPv4 based on DNS resolution. In a dual-stack deployment, hosts and network devices run IPv4 and IPv6 at the same time. Applications can query DNS and then select the protocol based on the returned records, such as using an AAAA record for IPv6 or an A record for IPv4. This gives the organization a controlled migration path because IPv6-capable applications and services can move to IPv6 while legacy IPv4 services remain reachable during the transition. Address-family translation for public web presence is useful when IPv6-only and IPv4-only endpoints must communicate through a translation boundary, but it does not provide native application choice between the protocols. Host-initiated tunnels and site-to-site IPv6-over-IPv4 tunnels encapsulate one protocol over another and add operational overhead. The question’s key phrase is that the application chooses between IPv6 and IPv4 based on DNS; that is the normal dual-stack behavior. Reference topics: IPv6 migration, dual stack, DNS A and AAAA records, transition strategy, application protocol selection.

Running BFD between EIGRP neighbors is the appropriate design when the problem is traffic loss during link failure and the requirement is to reduce the impact of the failure. EIGRP can detect neighbor loss through its hello and hold timers, but those timers may not be fast enough for applications sensitive to packet loss. Bidirectional Forwarding Detection provides rapid failure detection independent of the routing protocol’s normal timer expiration. When BFD detects a failed forwarding path, it notifies EIGRP so the routing process can converge without waiting for the EIGRP hold timer. Summarization is still a valuable scaling technique, but it primarily reduces route table size and query scope; it does not directly accelerate failure detection on an individual inter-router link. Reducing EIGRP hello and hold timers can improve detection, but it increases control-plane load and is less efficient than BFD. The question emphasizes data loss when any one link fails, so fast failure detection is the best corrective design. Reference topics: EIGRP convergence, BFD, failure detection, hello and hold timers, routed-link resiliency.