Cisco Designing Cisco Enterprise Networks Exam 300-420 ENSLD Exam Questions

Answer : A, D

The RPF check verifies that multicast traffic arrives on the interface the router would use to reach the source or RP, and it prevents forwarding when traffic arrives from the wrong direction. Cisco multicast forwarding is intentionally different from unicast forwarding because a multicast packet may need to be replicated toward many receivers. Without Reverse Path Forwarding, multicast loops and duplicate packets could occur. Option A captures the forwarding condition: the packet is accepted when it arrives on the interface used to route back toward the source address. Option D is the closest available drop condition in the answer set, expressing that packets not aligned with the correct reverse path are discarded rather than forwarded. Option B incorrectly checks the route toward the destination group, because multicast groups are not reached through ordinary unicast destination routing. Option C would flood traffic and create loops. Option E reverses the correct logic by dropping packets that arrive on the proper reverse-path interface. Reference topics: multicast RPF, loop prevention, source-tree forwarding, shared-tree forwarding, PIM.

Answer : A, D

Wake-on-LAN across routed boundaries requires directed broadcast handling toward the client subnet and helper behavior to forward the magic packet correctly. A sleeping host normally does not maintain a normal IP session, so the WoL magic packet is commonly sent as a directed broadcast to the destination subnet. Cisco designs therefore enable IP directed broadcast on the routed interface or SVI for the client subnet where the sleeping endpoints reside, while controlling the feature carefully to avoid abuse. The ip forward-protocol behavior is also relevant because routers must forward the required UDP broadcast traffic rather than dropping it at the Layer 3 boundary. In addition, an IP helper address toward the WoL server or relay path may be needed on client-facing interfaces so the magic packet can be delivered from the management or server subnet to the client subnet. PortFast helps endpoints become reachable quickly at Layer 2, but it does not replace routed broadcast forwarding. Reference topics: Wake-on-LAN, directed broadcast, ip helper-address, UDP forwarding, PortFast, campus services.

Answer : D

EIGRP with branch routers configured as stubs and equal-cost multipath is the best fit for this hub-and-spoke DMVPN design. The branch routers have limited memory and CPU resources, so they should not be forced to maintain unnecessary topology information or answer broad queries from the rest of the network. EIGRP stub routing limits the routes a branch advertises and prevents it from being used as a transit path, which reduces query scope and improves stability. Because the two internet links are both 100 Mbps, equal-cost multipath can use both links for active forwarding during traffic spikes. OSPF can operate over DMVPN, but a single area or hub-and-spoke design may create more overhead and less efficient query containment for small branch routers. IS-IS is less common for this WAN overlay use case, and iBGP with route reflectors can scale but does not natively consider link utilization or provide the same simple branch stub behavior. Reference topics: EIGRP stub, DMVPN, ECMP, branch routing, query containment, WAN convergence.

Answer : A, C

EIGRP and BGP are the two listed routing protocols that can support unequal-cost load balancing in Cisco enterprise designs. EIGRP performs unequal-cost load sharing by using the variance command. Feasible successor routes whose feasible distance falls within the variance multiplier can be installed alongside the successor route, provided they satisfy EIGRP loop-prevention rules. This allows traffic to use links with different composite metrics while still maintaining loop-free forwarding. BGP can also support unequal-cost distribution in specific designs, such as using BGP multipath features with additional bandwidth-based mechanisms or policy to influence traffic sharing across nonidentical paths. OSPF and IS-IS commonly support equal-cost multipath, but they do not natively perform EIGRP-style unequal-cost load balancing based on different path metrics. RIPng is also limited by hop-count behavior and is not used for unequal-cost multipath in this context. The correct design answer is therefore EIGRP and BGP. In production, the engineer must still validate hardware forwarding behavior, policy consistency, and whether the traffic-sharing method is per-flow or per-prefix.

Answer : D

In Cisco SD-Access, an intermediate node is an underlay transit device. Its responsibility is to provide IP reachability between fabric edge nodes, border nodes, and other fabric infrastructure roles. Intermediate nodes forward routed underlay traffic and do not perform endpoint registration, endpoint lookup, or VXLAN encapsulation for user traffic. Endpoint-to-location mapping is handled through the fabric control plane, which is based on LISP map-server and map-resolver functions. Fabric edge nodes identify connected endpoints, apply policy, act as anycast gateways, and encapsulate user traffic into VXLAN. Border nodes connect the fabric to external networks and handle traffic entering or leaving the fabric. The intermediate node is therefore comparable to a routed distribution or core transport device in a traditional hierarchical campus, except it is participating in the SD-Access underlay. It must provide stable Layer 3 reachability and appropriate MTU for encapsulated traffic but does not maintain the host tracking database or add security group information to VXLAN headers. The correct function is transporting IP packets between edge and border nodes.

Answer : D

The SD-Access underlay must run a routing protocol to establish IP connectivity between infrastructure devices. Cisco SD-Access uses a routed underlay to provide basic reachability among fabric edge nodes, border nodes, control-plane nodes, and intermediate nodes. Cisco design documentation states that all network elements in the fabric underlay must have IP connectivity through routing. Catalyst Center LAN Automation commonly deploys IS-IS for this purpose, although the underlay can be built manually with another supported routing design. The user endpoints and client subnets are not part of the underlay; they belong to the overlay, where fabric services, segmentation, and policy are applied. CEF should not be disabled, because efficient IP forwarding is necessary for the routed underlay. Two or more switches are not required merely to avoid spanning-tree loops; the SD-Access underlay is normally Layer 3 routed and avoids large Layer 2 loop domains. Reference topics: Cisco SD-Access underlay, routed access, LAN Automation, IS-IS, fabric node reachability.

Answer : B

The best design is the option that prefers ISP-1 for both outbound and inbound traffic while keeping ISP-2 available as a backup. For outbound traffic from the enterprise, local preference is the correct BGP attribute because it is evaluated inside the local AS and higher local preference wins. R1 should assign a high local preference to routes learned from ISP-1, while R2 should assign a low local preference to routes learned from ISP-2. For inbound traffic from the Internet toward the enterprise, AS-path prepending is the practical signal sent to external networks. Advertising routes to ISP-1 with no prepending and routes to ISP-2 with five prepends makes the ISP-1 path look shorter and therefore more attractive. The R1-to-R2 internal advertisements should not be blocked by NO-ADVERTISE because each edge router must still share reachability internally for failover. Option B matches these controls without unnecessarily suppressing routes between the edge routers. Reference topics: BGP local preference, AS-path prepending, active/backup Internet design, inbound and outbound path control.