300-420 Exam Dumps - Designing Cisco Enterprise Networks (ENSLD) v1.1

LISP is the control-plane protocol responsible for Endpoint Identifier to Routing Locator mapping in Cisco SD-Access. In the SD-Access architecture, an endpoint address is treated as an EID, and the fabric node location is represented by an RLOC. The fabric control-plane node performs LISP map-server and map-resolver functions so edge nodes can register local endpoints and resolve the current location of remote endpoints. This separation allows the overlay to support host mobility, anycast gateway behavior, and segmentation without depending only on traditional subnet-bound forwarding. VXLAN is the fabric data-plane encapsulation used to carry traffic across the fabric and preserve policy information, but it does not provide the EID-to-RLOC mapping function. CEF is the local forwarding mechanism inside Cisco devices, and GBAC is not the SD-Access mapping protocol. Therefore, LISP is the correct answer because it provides the SD-Access fabric control plane. Reference topics: Cisco SD-Access control plane, LISP, EID, RLOC, map-server, map-resolver.

Reverse Path Forwarding prevents multicast loops and duplicate packet forwarding. Multicast routing is source-oriented, so a router must verify that multicast traffic arrives on the interface it would use to reach the source or rendezvous point, depending on the tree state. If the packet arrives on the expected reverse-path interface, the RPF check succeeds and the router can forward the packet to the outgoing interface list. If it arrives on the wrong interface, the packet is dropped because accepting it could create a loop or duplicate stream. Cisco multicast designs rely on RPF checks with PIM to maintain loop-free distribution trees across redundant routed topologies. RPF does not notify upstream routers by itself, does not eliminate overlapping multicast group addresses, and is not simply a prune-generation mechanism. Prune behavior can occur as part of PIM tree maintenance, but the function asked here is loop prevention. Reference topics: multicast RPF check, PIM forwarding, source tree, shared tree, outgoing interface list, duplicate suppression.

Single-topology IS-IS with the transition feature is the correct design when IPv6 is being added to an existing IPv4 IS-IS network and both topologies must match exactly. In single-topology mode, IS-IS calculates one topology and uses it for both IPv4 and IPv6, which fits the requirement that the IPv4 and IPv6 paths and router levels remain the same on each interface. Cisco documentation notes that single-topology IS-IS IPv6 requires routers to run the same set of address families for adjacency consistency; during migration, transition support allows the network to operate while IPv6 is introduced gradually. Multi-topology IS-IS is used when IPv4 and IPv6 should be allowed to follow different topologies or when not all routers support the same address families. The question explicitly says the topologies will match exactly, so multi-topology is unnecessary. Single topology without the transition feature is risky during phased migration because routers that do not yet run both address families may fail adjacency checks or create blackholing. Reference topics: IS-IS for IPv6, single-topology IS-IS, transition mode, address-family consistency, IPv6 migration.

The EIGRP stub connected option is appropriate when the new circuit is intended to protect reachability to a connected subnet without turning the router into a broad transit point. EIGRP stub routing is used to limit the routes a router advertises to its neighbors and to constrain EIGRP query scope. A stub router can advertise connected routes, summary routes, redistributed routes, or combinations depending on the configured stub option. In this scenario, the new C-to-D circuit protects connectivity to 10.0.4.0/24 during a failure between B and D. Advertising the connected network through the stub behavior gives upstream routers a valid alternate route while still preventing unnecessary transit advertisements. Stub redistributed would be used for routes learned from another routing process, not for directly connected networks. Stub receive-only would prevent the router from advertising any routes, which would not protect reachability. Stub leak-map is used for controlled exceptions and is unnecessary if the required route is a connected subnet. Reference topics: EIGRP stub routing, connected route advertisement, query boundary design, DUAL stability.

Cisco SD-WAN is the correct solution when the design must use internet circuits at each site while providing failover, load sharing, and QoS. Basic IPsec tunnels can encrypt traffic, but they do not by themselves provide a complete WAN architecture for path measurement, dynamic traffic steering, centralized policy, application-aware routing, or scalable operational control. Cisco SD-WAN builds secure overlay tunnels across available transports and continuously measures path characteristics such as loss, latency, and jitter. It can then steer applications according to SLA policy, use multiple circuits for active/active forwarding, and fail traffic over when a path degrades or fails. QoS can be applied consistently through templates and policy across the WAN Edge routers. GET VPN is best suited to private MPLS-style networks and does not address internet-circuit overlay orchestration in the same way. Traditional DMVPN is a valid dynamic VPN technology, but SD-WAN is the more complete resilient internet-WAN design for these requirements. Reference topics: Cisco SD-WAN, internet transport, application-aware routing, failover, load sharing, QoS.

UplinkFast is the correct spanning-tree feature for faster convergence after an uplink failure in a classic STP access-layer design. UplinkFast is designed for access switches that have redundant uplinks toward the distribution layer. When the primary root port fails, UplinkFast allows an alternate blocked uplink to transition rapidly to forwarding, reducing the outage compared with standard 802.1D timer-based convergence. PortFast is used on edge ports connected to end hosts, not on switch-to-switch uplinks. Loop Guard protects against unidirectional failures or missing BPDUs on non-designated ports, but it does not accelerate recovery from an access uplink failure. BackboneFast helps when an indirect link failure is detected elsewhere in the topology, but the described failure is directly between SW1 and SW2. The design objective is the fastest possible convergence during that direct uplink loss, which matches UplinkFast in a traditional STP environment. Reference topics: Spanning Tree Protocol, UplinkFast, access-layer redundancy, root port failover, Layer 2 convergence.

As a STUN server, Cisco vBond allows Cisco Catalyst SD-WAN routers to discover their public mapped IP addresses and ports when they sit behind NAT. This function is essential during overlay bring-up because many WAN Edge devices are deployed behind internet circuits, firewalls, or provider NAT devices. vBond helps devices understand how they are seen from the public transport side and facilitates the formation of secure control connections to the SD-WAN controllers. vBond also participates in orchestration and Zero-Touch Provisioning workflows, but the question specifically asks about its purpose as a Session Traversal Utilities for NAT server. That wording points directly to NAT discovery, not general ZTP. vBond does not secure user data traffic between edge routers; data-plane encryption is established between WAN Edge devices. It also has no role in integrating SD-Access wireless into a fabric. Reference topics: Cisco SD-WAN vBond, STUN, NAT traversal, orchestration, WAN Edge onboarding. This is fundamental for internet transports.

An end-to-end QoS strategy with an SLA is the best fit for an application that cannot tolerate drops and requires very low latency across countries. The customer is asking for guaranteed service behavior, not just local classification on one router. A service line with an SLA defines the expected treatment across the provider network, including bandwidth, delay, jitter, and loss commitments. This is especially important for industrial or manufacturing applications that process large data chunks and are sensitive to packet loss. A purely domain-based PHB design can mark and forward traffic differently at each hop, but it does not by itself guarantee the business outcome unless backed by an end-to-end service agreement. A flow-based approach with per-flow queuing on every ISP node would consume more provider resources and scale poorly. FEC can help selected traffic but does not replace a QoS service model. Reference topics: QoS design, service-level agreements, end-to-end QoS, low-latency applications, loss-sensitive traffic, provider WAN services.