Cisco Updated 300-420 Exam Questions and Answers by rosemary

The selected IS-IS design must place the correct routers as Level 1/Level 2 boundary routers so that area failures stay local while traffic can still reach backbone application services. In a hierarchical IS-IS design, Level 1 routers exchange detailed topology only inside their own area. Level 2 routers form the backbone used for interarea connectivity. L1/L2 routers connect the local area to the backbone and advertise reachability between the two levels. Areas 20 and 30 are expected to double in size, and link flaps inside those areas must not impact the backbone. Therefore, the design should keep internal area routers at Level 1 and use only the boundary devices that connect those areas to the backbone as L1/L2. Option A matches that principle by selecting the appropriate boundary routers for interlevel connectivity while avoiding unnecessary L1/L2 adjacencies throughout the topology. The other options either place the wrong routers in Level 2 only or fail to provide a clean transition between local areas and the backbone. Reference topics: IS-IS hierarchy, L1/L2 boundary design, area containment, backbone stability, route leaking.

A single-homed full-mesh design is the best match when each WAN router has only one WAN interface, no additional WAN links can be purchased, and the customer still wants resilient site-to-site reachability. Single-homed means each site has one physical WAN attachment. Full mesh describes the logical connectivity model between sites, where each site can communicate directly with the others across the WAN service or overlay rather than relying completely on a central hub for intersite traffic. A hub-and-spoke design is simpler, but it creates dependency on the hub for spoke-to-spoke communication and provides poorer resiliency for a three-site design. Dual-homed hub-and-spoke and dual-homed full mesh both require additional WAN connectivity or interfaces, which violates the stated budget and hardware constraints. The best available design is therefore to use the single WAN attachment at each site while building a full-mesh logical topology over the provider or overlay service. Reference topics: WAN topology design, single-homed connectivity, full mesh, hub-and-spoke limitations, high availability under interface constraints.

PIM Source-Specific Multicast is the correct multicast protocol when receivers can subscribe to traffic from known sources and the design must avoid rendezvous points. SSM uses the (S,G) model, where receivers explicitly join a multicast group from a specific source. Because the source is known at join time, the network does not need a shared tree or RP discovery process. This makes SSM attractive for broadcast-style streaming applications, such as video channels, where each stream source is known and receivers subscribe to specific channels. PIM Sparse Mode and Any-Source Multicast use an RP to allow receivers to discover active sources, so they do not meet the requirement of no rendezvous point. BIDIR-PIM also relies on an RP-rooted shared tree and is optimized for many-to-many applications rather than source-specific broadcast channels. For a large cable TV provider streaming multiple video channels from defined sources, SSM simplifies the multicast control plane, eliminates RP dependency, and scales efficiently by creating only the source-specific state required by active receivers.

Dial-In: collector initiates a session to the device; supports gRPC only. Dial-Out: device initiates a session to the collector; supports TCP, UDP, and gRPC.

Model-driven telemetry can be deployed in dial-in or dial-out mode, and the difference is which side initiates the session and where the subscription is controlled. In dial-in mode, the collector initiates the session to the network device and requests the telemetry subscription. This makes the collector responsible for establishing the session and asking for the data stream. In the context of the provided options, dial-in is paired with support for gRPC only. In dial-out mode, the network device initiates the session toward the collector according to a configured subscription. This is useful when devices sit behind NAT or when the operational model requires devices to push telemetry to a known collector. In the provided choices, dial-out is paired with support for TCP, UDP, and gRPC. The mapping is not arbitrary; it follows Cisco telemetry terminology, where dial-in is collector-initiated and dial-out is device-initiated. This distinction is important in network automation designs because firewall policy, collector scaling, and subscription lifecycle management differ between the two modes.