300-420 Exam Dumps : Designing Cisco Enterprise Networks

Forward error correction and quality of service are the two listed techniques that directly improve application experience in a Cisco SD-WAN design. Forward error correction protects selected application traffic by sending recovery information so packet loss can be corrected without waiting for retransmission. That is especially useful for real-time voice and video traffic, where retransmission delay can degrade quality. QoS improves application treatment by classifying, marking, queuing, shaping, and prioritizing traffic according to business intent and application sensitivity. Cisco SD-WAN designs commonly combine application-aware routing, QoS, and loss-mitigation features to keep critical traffic on the best path and preserve service quality during congestion or impairment. A stateful firewall, AMP, and Cisco Umbrella improve security posture, but they do not primarily improve application experience in the forwarding-quality sense asked by the question. They may protect applications, but they do not directly address loss, delay, jitter, and congestion treatment. Therefore, FEC and QoS are the best answers. Reference topics: Cisco SD-WAN application experience, FEC, QoS, loss mitigation, real-time traffic handling.

Cisco SD-WAN uses Path MTU Discovery to avoid fragmentation problems across the overlay. SD-WAN traffic is encapsulated and encrypted, which adds overhead beyond the original packet size. If the effective path MTU is smaller than the encapsulated packet, fragmentation or packet loss can occur, especially when the DF bit is set or when intermediate devices block fragmentation-related ICMP messages. PMTUD allows devices to discover the largest packet size that can traverse the path without fragmentation and adjust forwarding behavior accordingly. Marking traffic with DF alone does not solve the issue; it may expose the problem by causing packets to be dropped when too large. Jumbo frames are not a universal WAN solution because service-provider, Internet, and broadband paths often do not support them consistently. Configuring every access circuit with a fixed 1600-byte MTU is not a reliable design assumption. The correct design is to rely on PMTUD and validate tunnel overhead, device MTU, TCP MSS adjustment where needed, and ICMP handling across transports. Reference topics: Cisco SD-WAN MTU, PMTUD, tunnel overhead, fragmentation avoidance, IPsec encapsulation.

An MPLS WAN from two separate ISPs is the strongest fit when the enterprise requires an active/backup WAN design with guaranteed SLAs for applications on either connection. MPLS VPN services are typically delivered with provider-backed service-level commitments for latency, jitter, packet loss, and availability, which is why they are selected for predictable enterprise application transport. Using two separate MPLS providers improves resiliency against a provider failure while preserving SLA-backed behavior on the backup path. A hybrid MPLS and Internet VPN model can be cost effective, but the Internet path generally does not provide the same deterministic SLA unless enhanced by a specific managed service contract. Internet from two providers improves reachability diversity but does not inherently guarantee application SLA. A single ISP hybrid design creates a provider dependency and weakens availability. Therefore, dual-provider MPLS is the conservative design for guaranteed active/backup WAN service. Reference topics: MPLS WAN design, service-level agreements, active/backup WAN, provider diversity, application performance assurance.