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

Contracting an internet connection and deploying DMVPN is the most practical solution when the enterprise needs a fast, affordable, and reliable backup for a single MPLS provider. DMVPN can use broadband internet transport to build encrypted GRE/IPsec tunnels between sites, providing a backup WAN path without waiting for another private MPLS provider circuit. It supports dynamic routing and can be deployed incrementally, which makes it suitable after a recent outage when time and cost matter. BFD echo mode toward a provider PE can improve failure detection, but it does not create an alternate transport if the only MPLS provider has an outage. Adding a WAN router and a floating static route also fails unless another path exists. Contracting a second MPLS provider and deploying GETVPN may be robust, but it is slower and more expensive than the requested quick and affordable backup. Reference topics: DMVPN backup WAN, MPLS resiliency, internet VPN, IPsec, branch availability, rapid WAN deployment.

Affinity is the Cisco SD-WAN feature used to minimize TLOC and control connections and reduce strain on vSmart controllers. Cisco documentation explains that establishing affinity between controllers and edge devices allows the operator to control overlay scaling by limiting which controllers an edge device can establish control connections with. In large deployments, unrestricted connections between every WAN Edge and every controller can create unnecessary state and operational load. Affinity lets the design distribute edge connections across controllers and data centers while still preserving redundancy through primary and backup controller relationships. Color identifies the transport type or behavior associated with a TLOC, but it does not reduce controller connection scale by itself. Control-direction and control-connections are not the feature names that provide the scaling function described in the question. A well-designed SD-WAN control plane uses affinity, controller groups, and redundancy planning to keep the overlay scalable and predictable. Reference topics: Cisco SD-WAN affinity, vSmart controller scale, TLOC connections, control-plane redundancy, overlay scaling.

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.