What 300-420 Questions and Answers feature?

Option A is the best addressing design because it gives each site enough capacity while avoiding excessive address waste and supporting summarization. A campus requiring 12,000 devices needs at least 14 host bits because 2^13 minus two is only 8190 usable addresses, while a /18 provides 16,382 usable addresses. That leaves room for growth without assigning an unnecessarily huge block. Each branch requiring 1,000 devices needs at least 10 host bits; a /22 provides 1,022 usable addresses, but /21 provides 2,046 usable addresses and additional growth capacity. The selected branch blocks, 10.0.192.0/21 and 10.0.200.0/21, are contiguous on valid /21 boundaries and can be summarized cleanly where appropriate. Option D fails because a /20 supports only 4094 usable addresses and cannot accommodate the 12,000-device campus. Option B overallocates a /16 to the campus and /20s to branches, wasting resources. Option C is grossly oversized and operationally poor. Reference topics: hierarchical IPv4 addressing, route summarization, VLSM, host-capacity planning, convergence containment.

Manual underlay is the correct deployment approach for a brownfield SD-Access scenario. In a greenfield fabric, Cisco DNA Center LAN Automation can build the routed underlay by discovering devices, assigning addresses, and creating the required underlay adjacencies. Brownfield environments already have an installed campus network, addressing plan, routing policy, operational constraints, and production dependencies. Rebuilding that underlay automatically can introduce unnecessary disruption. Cisco SD-Access brownfield designs normally preserve and validate the existing routed underlay, then use Cisco DNA Center to discover devices and automate the fabric overlay, policy, and endpoint segmentation functions. Subnet stretching is not the required deployment model and can create operational complexity. Automated underlay and LAN automation are powerful when the physical network is being newly built, but they are not the safest default for an established production environment. A professional brownfield design should first confirm MTU, routing reachability, loopback advertisements, device support, and fabric readiness before onboarding nodes. Reference topics: SD-Access brownfield migration, manual underlay, Cisco DNA Center, LAN Automation, fabric readiness.

The design should use a scavenger queue for excessive or suspicious traffic and apply queuing on the access-to-distribution uplinks where congestion can occur. Cisco QoS campus design commonly uses a less-than-best-effort scavenger class to constrain traffic associated with worms, peer-to-peer applications, bulk background flows, or other nonbusiness traffic. Placing this traffic in a scavenger queue minimizes the bandwidth it can consume during congestion without harming real-time applications. Real-time voice or video traffic should be placed in a strict-priority queue so it receives low delay and low jitter treatment when links are congested. Applying queuing on access-to-distribution links is important because those uplinks are common campus congestion points, especially during bursts or abnormal traffic events. A shaping policy is not the right tool for campus LAN uplinks, and indiscriminate policing of real-time traffic can cause drops that damage voice and video quality. Reference topics: campus QoS, scavenger class, strict-priority queue, access uplink queuing, congestion management, worm mitigation.