Free Cisco 300-420 Practice Exam with Questions & Answers | Set: 12

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.

The fabric control plane in Cisco SD-Access creates and resolves endpoint-to-location mappings. SD-Access separates endpoint identity from physical topology by using LISP in the control plane. Endpoint addresses are treated as Endpoint Identifiers, and fabric node locations are represented by Routing Locators. When an endpoint appears on a fabric edge node, the edge registers that endpoint-to-edge binding with the control-plane node. When another edge needs to send traffic to that endpoint, it queries the control plane to resolve the current location and then uses the fabric data plane to encapsulate traffic toward the correct destination. Group-Based Access Control policy creation and enforcement involve Cisco ISE, security group tags, and policy components rather than the basic mapping purpose of the fabric control plane. BGP route reflection is not the SD-Access control-plane function, and extending multiple subnets to one RLOC is not the main purpose. Reference topics: SD-Access control plane, LISP, EID-to-RLOC mapping, endpoint registration, map resolution.

When congestion is sustained and QoS has already been optimized, the correct design response is to add capacity rather than continue tuning packet treatment. QoS manages contention by prioritizing, queuing, shaping, or dropping traffic, but it does not create additional bandwidth. If access-to-distribution uplinks are persistently oversubscribed, business applications will still suffer because the offered load exceeds the available link capacity. Implementing higher-speed uplink interfaces increases the physical bandwidth available for aggregate traffic. Bundling additional uplinks into EtherChannels also increases usable capacity and improves resiliency while presenting a single logical link to the switching and routing design. Random early detection and selective packet discard can improve queue behavior under congestion, but the question states that QoS is already optimized and no longer effective. Reconfiguring QoS to IntServ would add complexity and is not a realistic campus fix. Therefore, the architect should increase uplink capacity through faster links and EtherChannel where the hardware and cabling support it. Reference topics: campus oversubscription, EtherChannel, uplink capacity planning, QoS limitations, congestion remediation.