300-420 Exam Dumps - Cisco CCNP Enterprise Questions and Answers

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.

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.

The correct solution is IntServ with RSVP. The requirement says the application must be able to request a specific service level and receive guaranteed bandwidth with support for delay requirements. Cisco describes Integrated Services as a QoS model that uses Resource Reservation Protocol to signal per-flow resource requirements across the network. RSVP allows applications or endpoints to request bandwidth and delay treatment; each participating network device can admit or reject the reservation based on available resources. This is exactly the behavior needed when an application must explicitly request a service profile rather than simply inherit a class marking. DiffServ with DSCP is more scalable, but it only marks traffic and applies class-based per-hop behavior. It does not provide per-flow reservation or allow the application to explicitly reserve resources. DSCP by itself is a marking mechanism, not a reservation protocol. RSVP belongs with IntServ in the classic QoS model. Reference topics: Integrated Services, RSVP, resource reservation, QoS guarantees, delay-sensitive applications.

The correct solution is a management VRF with SSH keys for device access. A management VRF creates a separate routing and forwarding table for management traffic, keeping administrative reachability isolated from production and overlay routes. That directly satisfies the requirement that the overlay network must not cause routing issues and makes troubleshooting easier for operations teams because management reachability can be validated independently. Cisco VRF design uses separate routing tables to isolate traffic and can support overlapping addresses or independent routing policy. For secure device access, SSH with key-based authentication provides encrypted administrative sessions and stronger authentication than clear-text or password-only methods. Private VLANs and ordinary VLANs provide Layer 2 separation but do not create independent routing tables. TACACS+ and RADIUS are AAA systems; they are useful but do not define the management transport architecture. Separate physical interfaces can be useful out-of-band, but the best match for overlay isolation and operational simplicity is management VRF plus SSH keys. Reference topics: management VRF, secure device access, SSH public-key authentication, routing-table isolation, enterprise management design.

Cisco IS-IS supports Level 1, Level 2, and Level 1/Level 2 operation, and the design should restrict each link to the level it actually needs. Cisco documentation for the isis circuit-type command states that it “configures the type of adjacency that is required for neighbors on the specified interface.” In this case, the router is configured as L1/L2 and has both L1 and L2 neighbors, which causes unnecessary LSP flooding, SPF processing, and database maintenance on links that may not need both levels. Making the entire router only L1 or only L2 would be too blunt, because the router may legitimately need to participate in both domains on different interfaces. Making the router a DIS also does not solve the underlying issue; it only controls designated intermediate system behavior on broadcast networks. The best optimization is to configure each interface with the correct circuit type, such as level-1 for intra-area links and level-2-only for backbone links. This reduces control-plane load while preserving the intended two-level hierarchy.

The design combines Dual-Stack Lite from the devices toward the core MPLS network and NAT44/64 from the MPLS network toward the Internet gateway router. The requirements describe IPv6-facing clients that still need access to IPv4 services and DNS behavior that allows the same service name to be reached during migration. Dual-Stack Lite carries IPv4 customer traffic across an IPv6 access or provider network by tunneling IPv4 packets over IPv6 toward a provider translation point. NAT44/64 services then provide translation or address-family interworking for IPv4-only resources. This combination is used when customer-facing access moves to IPv6 while legacy IPv4 services remain reachable during transition. A simple IPv6 tunnel from devices to the MPLS core does not provide the required IPv4 service translation. Using only NAT44/64 from end devices also shifts complexity to clients rather than placing translation at the network edge. The selected choices match the staged migration model: IPv6 transport with encapsulation in the access/core side and translation at the provider or gateway boundary. Reference topics: IPv6 transition, DS-Lite, NAT64, DNS64, IPv4-over-IPv6 tunneling.

Traffic shaping is the QoS mechanism that queues excess packets and transmits them later to conform to a configured rate. In Cisco QoS design, shaping smooths bursts by buffering traffic instead of immediately discarding it when the offered rate exceeds the configured rate. This makes shaping appropriate on egress interfaces where the enterprise router has a higher physical interface speed than the actual provider committed information rate. WRED and RED are congestion-avoidance mechanisms that drop packets probabilistically to prevent full queue exhaustion, especially for TCP traffic. They do not intentionally hold excess packets for later transmission as the primary behavior. Policing enforces a traffic rate by dropping or remarking traffic that exceeds the configured contract; it does not buffer traffic to smooth bursts. Therefore, when the design requirement says excess packets must be queued for later transmission, the mechanism must be shaping. In WAN edge QoS, shaping is often paired with child queuing policies so latency-sensitive and business-critical classes receive correct treatment inside the shaped parent rate.

Nonstop Routing is the correct solution when the upstream router does not understand graceful restart messaging. Cisco NSF and graceful restart depend on helper behavior from neighboring routers. During a supervisor switchover, the restarting device asks neighbors to preserve forwarding and adjacency state while the control plane recovers. If the neighbor does not support or understand the graceful restart signaling, NSF cannot deliver the intended benefit and route recomputation may still occur. NSR is different because it synchronizes routing protocol state between the active and standby supervisor internally, allowing the switch to preserve routing operation during stateful switchover without requiring graceful restart support from the neighbor. Remote LFA FRR protects against data-plane failures by precomputing repair paths, but it does not address supervisor switchover route recomputation. Aggressive IS-IS timers may make failure detection faster, but they increase control-plane churn and do not solve the lack of graceful-restart helper support. Therefore, the Catalyst switch should use NSR for this design. Reference topics: IS-IS high availability, NSR, NSF, graceful restart helper support, stateful switchover.

The design must enable IPv6 multi-topology behavior at the appropriate edge routers and move metric handling toward transition support where the current IS-IS network still uses narrow metrics. Multi-topology IS-IS is important during IPv4-to-IPv6 migration because IPv4 and IPv6 reachability do not always exist on identical links at every stage of the migration. If IPv6 follows the IPv4 topology when some devices or paths are not IPv6-ready, traffic can be blackholed. Multi-topology allows independent IPv4 and IPv6 SPF calculations, which prevents IPv6 traffic from being forwarded through IPv4-only portions of the network. The metric-style transition setting is used when migrating from narrow to wide metrics, allowing interoperability while routers are upgraded and the design scales. Because the requirement says IPv6 areas will grow and the current network uses narrow metrics, the selected edge devices must support the IPv6 topology and metric transition behavior shown in the exhibit. Reference topics: IS-IS IPv6, multi-topology IS-IS, narrow metrics, wide metric transition, IPv6 migration, blackhole prevention.

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.