Free Practice Questions for Cisco 300-420 Exam

The drag-and-drop mapping identifies which elements belong to each model-driven protocol or data-modeling mechanism. Cisco programmability designs distinguish the data model, the encoding, and the transport protocol. YANG defines the structure of configuration and operational data. NETCONF commonly uses XML encoding and provides transactional operations such as get-config, edit-config, lock, and commit-like workflow depending on platform support. RESTCONF exposes YANG-modeled data through HTTP methods and typically uses URI-based resources with XML or JSON encoding. gRPC and gNMI are commonly used for efficient telemetry or operational data streaming, with protocol buffers often used for serialization. The selected mapping follows those protocol boundaries rather than mixing model structure with transport behavior. In design work, this matters because the same network feature can be represented by a YANG model but accessed through different protocols, each with different capabilities, security requirements, and operational semantics. Correctly matching elements to protocols avoids invalid payloads and broken automation workflows. Reference topics: YANG, NETCONF, RESTCONF, gRPC, gNMI, XML and JSON encoding, model-driven telemetry.

The OSPF design should include LSA/SPF timer tuning and summarization with appropriate stub-area design. Cisco OSPF convergence is affected by failure detection, LSA generation, flooding, SPF scheduling, and routing-table installation. Tuning LSA and SPF throttling timers helps the network react quickly to genuine failures while avoiding excessive CPU churn during repeated flaps. This is especially important when voice and video traffic are sensitive to convergence delay. Manual route summarization at area boundaries reduces the number of detailed routes advertised between areas and limits the blast radius of link failures. Configuring nonbackbone areas as stub networks where appropriate also reduces external LSA propagation and lowers router resource use. Reducing DR and BDR election frequency is not a primary design tool for convergence, and increasing hello and hold timers would slow failure detection rather than improve it. Advertising default routes can be useful, but it does not by itself contain link flap impact. Reference topics: OSPF area design, LSA throttling, SPF throttling, route summarization, stub areas, convergence optimization.

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.

Spanning-tree PortFast must be enabled on interfaces where Wake-on-LAN clients reside so the PCs become reachable immediately when they power on. WoL depends on a sleeping endpoint receiving a magic packet, and once the device wakes, it must be able to send and receive traffic without waiting through traditional STP listening and learning states. Cisco campus designs commonly enable PortFast on access ports connected to end hosts so those ports transition directly to forwarding. That reduces login, DHCP, and application delays after a host becomes active. The NIC and system firmware must support WoL, but the option stating that WoL should be disabled in BIOS is technically wrong. IP directed broadcast and UDP forwarding are relevant when WoL packets must cross routed boundaries, but the answer options here focus on a single action to prevent client-side delay. Disabling directed broadcast or forward protocol would work against remote WoL operation. Reference topics: Wake-on-LAN, PortFast, access-layer design, STP edge ports, client startup convergence.

Lowering the OSPF cost on the direct R1-to-R2 link is the cleanest way to force traffic for 10.10.20.0/24 to prefer that link. OSPF calculates the shortest path using cumulative interface cost, and Cisco designs normally tune OSPF path selection by changing interface cost rather than administrative distance. Administrative distance determines preference between different routing protocols, not between OSPF paths inside the same OSPF process. Moving the link into another area or creating a multiarea adjacency adds design complexity and does not directly solve the requirement unless the resulting cost still becomes lower. The exhibit states that the architect must use the direct link for traffic from 10.10.10.0/24 toward 10.10.20.0/24. Therefore, the direct link must have a lower total OSPF metric than the alternate path. Configuring the link cost to a value below 30 makes OSPF choose it as the preferred intra-area route. This is deterministic, easy to validate with the OSPF database and routing table, and consistent with Cisco hierarchical IGP design practice. Reference topics: OSPF cost, SPF path selection, metric tuning, intra-area routing.

A single-homed enterprise that runs BGP with one ISP should advertise its assigned public prefix to the ISP and receive a default route from the ISP. Because there is only one upstream provider, the customer does not need the full Internet table to make path-selection decisions; all Internet destinations exit the same provider path. Receiving only a default route conserves memory and CPU on the CE router and simplifies operations. The customer must still originate its public prefix toward the ISP so the provider can advertise reachability to the Internet. The ISP should not be the originator of the customer-owned ARIN prefix toward the customer; it may advertise that prefix to the Internet after receiving it from the customer. Requesting the full BGP table or even a partial table adds unnecessary scale for a single-homed site. Advertising a default route to the ISP is also wrong because the ISP already owns upstream Internet reachability. Reference topics: single-homed BGP, CE-PE peering, default route, public prefix advertisement, Internet edge design.

The required BGP address family is L2VPN EVPN. The design calls for VXLAN over a Layer 3 IPv4 fabric while preserving Layer 2 adjacency and allowing workload mobility between sites. EVPN is the BGP control plane used with VXLAN overlays to advertise MAC reachability, IP host information, and Ethernet segment information in a scalable way. It separates the Layer 2 and Layer 3 overlay control plane from the underlay IGP, which in this case is OSPF. VPNv4 is used for MPLS Layer 3 VPN routes, not VXLAN Layer 2 adjacency. IPv4 unicast advertises ordinary IP prefixes and does not carry MAC mobility or Ethernet VPN information. L2VPN VPLS or VPWS address families are associated with MPLS-based Layer 2 VPN services and do not provide the VXLAN EVPN control-plane model required here. EVPN is therefore the correct family for VXLAN fabrics that need host mobility and scalable Layer 2 extension. Reference topics: BGP EVPN, VXLAN, L2VPN EVPN address family, MAC reachability, workload mobility.

The correct get-config reply is the one that shows OSPF process ID 200 and the network 172.16.10.128/26 assigned to Area 0 in the same YANG model hierarchy that was used for configuration. In model-driven configuration, verification is not based on visual similarity to CLI output; it is based on whether the operational or running datastore contains the intended structured objects at the correct schema paths. For IOS XE native OSPF configuration, the process identifier, network statement, wildcard or prefix representation, and area association must be represented exactly as the model requires. A /26 network beginning at 172.16.10.128 covers addresses 172.16.10.128 through 172.16.10.191, so replies showing a different base network, wrong process ID, wrong area, or invalid mask cannot verify the design. Option A is the matching reply. The professional validation workflow is to send the configuration, read back the intended datastore using get-config, and confirm the model fields rather than relying only on CLI screen output. Reference topics: NETCONF get-config, IOS XE native OSPF YANG, datastore verification, OSPF area configuration.

The correct policy is to prepend the AS path on the nonpreferred advertisement for each prefix. For inbound BGP traffic engineering, the enterprise normally influences remote autonomous systems by changing attributes that those systems see when selecting a path. AS-path prepending makes a route appear less attractive by adding repeated instances of the local AS number to the AS path. In this design, network 10.1.1.0/24 should enter through R3-R1, so R2 must advertise that prefix with a prepended AS path to make the R4-R2 path less preferred unless the primary path fails. Conversely, network 10.1.2.0/24 should enter through R4-R2, so R1 must advertise that prefix with prepending to make the R3-R1 path less preferred. This creates inbound load sharing while preserving failover because the prepended route remains available as a backup. Local preference affects outbound path selection inside the local AS, not inbound selection by the provider. Reference topics: BGP traffic engineering, AS-path prepending, inbound path control, prefix-specific policy, multihomed WAN design.

VPN 0 is the transport VPN in Cisco SD-WAN. It carries control traffic and provides connectivity from WAN Edge routers toward the transport networks, such as MPLS, Internet, LTE, or other WAN services. Control connections to Cisco SD-WAN controllers are established through transport interfaces that belong to VPN 0. Data VPNs carry service-side user traffic and are separate from the transport VPN. VPN 512 is commonly used for out-of-band management, not for carrying overlay control connections. VPN 128 and VPN 256 are not the reserved transport VPN identifiers. The design importance is that VPN 0 must have correct addressing, color assignment, routing reachability, NAT traversal considerations, and certificate-based controller connectivity. If VPN 0 is misdesigned, the WAN Edge cannot establish stable control connections, cannot receive OMP routes and policies, and cannot build the secure overlay properly. Therefore, VPN 0 is the correct transport VPN for underlay control traffic. Reference topics: Cisco SD-WAN VPN 0, transport VPN, control connections, WAN Edge onboarding, overlay formation.