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

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.

Integrated Services is the QoS model that allows an application to signal its traffic requirements to the network and request specific service treatment. Cisco QoS guidance distinguishes IntServ from DiffServ by explaining that IntServ follows a signaled-QoS model, while DiffServ uses provisioned per-hop behavior based on markings. IntServ uses RSVP to reserve resources along the end-to-end path. That reservation process allows the network to admit or deny the flow based on available bandwidth and policy, which is why IntServ aligns with applications that require consistent and dedicated bandwidth. DiffServ is much more scalable and widely deployed in enterprise networks, but it does not provide per-flow resource reservation by itself. LLQ is a queuing mechanism commonly used inside a DiffServ design for delay-sensitive traffic such as voice. WRED is a congestion-avoidance technique, not an end-to-end reservation architecture. Because the question explicitly says that the application informs the network of its traffic profile and requests a service level, the correct QoS architecture is IntServ.

Cisco Catalyst SD-WAN separates orchestration from management, control, and data forwarding. The orchestration-plane function is provided by vBond, which authenticates WAN Edge devices and helps establish secure connectivity between edges and controllers. In Cisco design terms, vBond is also the NAT traversal facilitator because it allows devices sitting behind NAT to discover reachable public and private address information and form the correct control connections. These two functions match the options for primary authentication point and NAT traversal facilitation. Centralized provisioning, troubleshooting, monitoring, and template-based configuration belong to vManage, the management plane. Route and policy distribution belongs to vSmart, the control plane, through OMP. Zero Touch Provisioning is part of the onboarding workflow, but the question asks for orchestration-plane functions, not the broader provisioning service. A sound SD-WAN design should deploy redundant vBond instances, ensure DNS reachability to them, and validate firewall rules so DTLS/TLS control connections can be established reliably across Internet and private transports. Reference topics: Cisco SD-WAN architecture, vBond orchestration, control connections, NAT traversal.