Cisco Updated 300-420 Exam Questions and Answers by niya

The correct QoS design is to shape outbound traffic and police inbound traffic. Traffic shaping buffers and schedules outbound packets so the customer does not send bursts beyond the 10 Mbps Internet connection rate. This is useful on egress because the local router controls the transmit queue and can smooth bursts before they reach the provider. Cisco QoS design distinguishes shaping from policing: shaping delays excess traffic, while policing drops or remarks excess traffic immediately. Inbound shaping is generally not effective because the traffic has already arrived on the interface; the device cannot delay packets before they consume the inbound circuit. Inbound policing can protect business-critical traffic by limiting or dropping lower-priority excess traffic as it enters the network. Policing outbound would enforce the rate but would cause avoidable drops during bursts, which is less desirable when the router can shape before transmission. Therefore, outbound shaping and inbound policing satisfy both rate-control and protection requirements. Reference topics: traffic shaping, traffic policing, QoS queuing, Internet edge QoS, congestion management.

The two practical OSPF convergence improvements are enabling Bidirectional Forwarding Detection and tuning OSPF timers and throttling behavior. Cisco describes BFD as a protocol designed to provide fast forwarding-path failure detection across media, encapsulations, topologies, and routing protocols. With OSPF, BFD allows a neighbor failure to be detected rapidly without depending only on the OSPF dead interval. OSPF parameters can also be tuned, including SPF scheduling, LSA generation, and LSA arrival throttling, so the control plane reacts quickly but not recklessly during instability. Merging all areas into one backbone area is not a convergence improvement; it usually increases the size of the link-state database and the impact of topology changes. Making every nonbackbone area stub may reduce external LSA scope, but it is not universally valid and does not directly solve failure detection. Spanning the same IP network across multiple OSPF areas is a poor design and can create operational ambiguity. Therefore, BFD plus careful OSPF parameter tuning are the appropriate convergence-focused design actions.

For point-to-point telepresence, asymmetric routing can create delay variation, packet reordering, and troubleshooting complexity. The design requirement is to make egress and ingress flows follow the same path. In the topology, the best way to steer traffic away from the less desirable return path is to configure a higher metric on the router in area 4 so OSPF path selection favors the symmetric path. OSPF chooses paths based on cumulative cost, and increasing the cost on the unwanted path makes the preferred path more attractive without removing redundancy. Route leaking on the routers in area 1 or area 2 would introduce additional interarea route visibility but would not necessarily solve the asymmetric flow problem. A route filter in area 4 could remove reachability or create suboptimal failure behavior rather than simply preferring the right path. Raising the metric is a cleaner design technique because it preserves backup reachability while influencing normal forwarding. Reference topics: OSPF cost design, symmetric routing, telepresence traffic, interarea path optimization, metric engineering.

The correct routing design is OSPF with multiple areas. The company is moving away from RIP because the network has grown and now requires segmentation, summarization, fast convergence, and scalability. Cisco positions OSPF as a link-state IGP suitable for larger enterprise networks, and OSPF areas are the standard mechanism for containing topology information and scaling the link-state database. Area Border Routers can summarize routes between areas, reducing routing table size and limiting the scope of link-state flooding and SPF recalculation. This directly satisfies the requirement to segregate departments while summarizing between segments. EIGRP can converge quickly and summarize, but “stub areas” are not an EIGRP construct; EIGRP uses stub routers. OSPF virtual links are not a primary segmentation design tool; they are used to repair backbone connectivity issues. Modifying EIGRP K values changes metric calculation but does not solve segmentation or summarization. Reference topics: OSPF multi-area design, ABR summarization, SPF scope control, enterprise IGP scalability.