300-420 Exam Dumps : Designing Cisco Enterprise Networks

Implementing network summarization on the edge routers is the correct EIGRP design action to reduce query range and improve convergence. In EIGRP, when a route is lost and no feasible successor exists, DUAL sends queries to neighbors. If the network is large or poorly summarized, those queries can propagate widely and increase convergence time. Hierarchical addressing allows each office or edge block to advertise a summary instead of many specific prefixes. If a specific subnet inside an office fails, the summary can remain stable toward the rest of the network, preventing the failure from triggering unnecessary queries across the dark-fiber interoffice topology. Stub routing can also reduce query scope, but the option says to configure stub areas on non-edge routers, which is not the right EIGRP terminology or placement. Different EIGRP processes add redistribution complexity, and route filtering alone does not provide the same clean convergence boundary as summarization. Reference topics: EIGRP summarization, DUAL query scope, hierarchical addressing, convergence optimization, dark-fiber campus routing.

BFD is the correct design feature for detecting a link failure within 200 ms or less without materially increasing OSPF control-plane load. Cisco uses Bidirectional Forwarding Detection as a fast, lightweight failure-detection protocol that can be associated with routing protocols such as OSPF. Instead of relying on aggressive OSPF hello and dead timers, BFD performs rapid forwarding-path checks and notifies OSPF when the path fails. This allows fast convergence while avoiding the additional routing-protocol overhead and instability that can come from very low hello timers. UDLD detects unidirectional Layer 2 fiber failures, but it is not the routing adjacency failure-detection mechanism requested here. Carrier delay can adjust interface state transition timing, but it does not provide a routing-protocol independent liveness session. Fast hellos can reduce detection time, but they increase protocol traffic and can affect overall performance. BFD is therefore the proper design choice for fast and efficient OSPF convergence. Reference topics: BFD, OSPF convergence, fast failure detection, routed campus resiliency, control-plane efficiency.

StackWise is the correct solution because the company needs more access ports while reusing the existing access-switch uplink capacity. Cisco StackWise allows multiple compatible Catalyst switches to operate as a single logical switching system, increasing access-port density without requiring each added switch to consume new uplink ports on the distribution layer. This fits the design constraint that the distribution switches have no available ports for additional uplinks, while current uplink bandwidth is not a bottleneck. VSS is normally used to combine two chassis-class switches into one logical system at the distribution or core layer; it is not the practical answer for expanding one floor’s access-port count from an existing access switch. EtherChannel aggregates physical links for bandwidth and redundancy, but it does not create additional access ports when no distribution ports are available. VDC is a Nexus virtualization construct and does not solve Catalyst access-port expansion. The correct operational design is to add a stack member and use the existing uplink design. Reference topics: Cisco StackWise, access-layer scalability, uplink preservation, Catalyst campus switching.