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

L2VPN is the correct technology because the requirement is for two remote offices to share a common broadcast domain across a private WAN with minimal overhead. A Layer 2 VPN service extends Ethernet or VLAN connectivity between customer sites while keeping the customer routing design independent of the provider core. From the customer perspective, the two sites can appear to be on the same Layer 2 segment, which satisfies the shared broadcast-domain requirement. GET VPN, IPsec, and GRE are Layer 3-oriented technologies. They can connect sites securely or provide tunneling, but they do not natively create a common Layer 2 broadcast domain between the offices. GRE also adds additional encapsulation overhead, and IPsec alone generally provides encrypted routed connectivity rather than an Ethernet service. For a simple direct logical path over a private WAN, an L2VPN service such as VPWS or VPLS is the appropriate design family. Reference topics: L2VPN, VPWS, VPLS, Ethernet WAN services, broadcast-domain extension, private WAN connectivity.

Route summarization should be planned from the aggregation layer toward both the core and the access layer. In hierarchical campus routing, aggregation or distribution devices are natural summarization boundaries because they sit between more specific access-layer networks and the core. Summarizing from aggregation toward the core prevents access-layer subnet churn from forcing unnecessary recomputation and route table growth in the core. Summarizing from aggregation toward access can also provide a concise upstream route, often a default or summary route, so access devices do not need the entire network routing table. The goal is to contain failures, reduce routing state, and preserve fast convergence at hierarchy boundaries. Summarizing from the core toward aggregation may hide useful topology details in the wrong direction, while summarizing directly from access toward aggregation is not always possible or efficient when access devices are numerous and have limited resources. The answer that places summarization at aggregation in both directions best matches Cisco hierarchical design principles. Reference topics: hierarchical campus design, route summarization, aggregation layer, core route scale, convergence containment.

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.