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

Dual stack is the correct migration strategy when the application chooses IPv6 or IPv4 based on DNS resolution. In a dual-stack deployment, hosts and network devices run IPv4 and IPv6 at the same time. Applications can query DNS and then select the protocol based on the returned records, such as using an AAAA record for IPv6 or an A record for IPv4. This gives the organization a controlled migration path because IPv6-capable applications and services can move to IPv6 while legacy IPv4 services remain reachable during the transition. Address-family translation for public web presence is useful when IPv6-only and IPv4-only endpoints must communicate through a translation boundary, but it does not provide native application choice between the protocols. Host-initiated tunnels and site-to-site IPv6-over-IPv4 tunnels encapsulate one protocol over another and add operational overhead. The question’s key phrase is that the application chooses between IPv6 and IPv4 based on DNS; that is the normal dual-stack behavior. Reference topics: IPv6 migration, dual stack, DNS A and AAAA records, transition strategy, application protocol selection.

The Cisco SD-Access component mapping is based on the normal fabric roles. A fabric edge node is the access-facing fabric device that connects wired endpoints and fabric access points, acts as the anycast Layer 3 gateway, encapsulates endpoint traffic into VXLAN, and registers endpoint reachability with the control plane. A control-plane node supplies the LISP map-server and map-resolver functions, maintaining endpoint-to-location mappings. A border node connects the fabric to external Layer 3 domains, shared services, WAN, Internet, or another fabric/transit domain, and it de-encapsulates traffic as it leaves the fabric. Intermediate nodes provide routed IP transport inside the underlay and move packets between edge, border, and control-plane nodes without owning endpoint policy or registration. This role separation is important because a design failure often comes from assigning the wrong function to the wrong node. Access-facing policy and endpoint onboarding belong at the edge; external connectivity belongs at the border; location resolution belongs to the control plane; transport belongs to intermediate nodes. Reference topics: SD-Access fabric roles, edge node, border node, control-plane node, intermediate node.

BGP outbound route filtering is the correct solution because the enterprise wants control over which routes it receives without waiting for a provider change cycle each time the prefix set changes. Cisco BGP prefix-based ORF allows a receiving BGP speaker to send an inbound prefix-list filter to the remote peer, which then applies that list as an outbound filter. This reduces unwanted routing updates before they cross the session and lets the enterprise update the desired prefixes locally when business requirements change. Requesting only fixed prefixes from the ISP would work initially but fails the flexibility requirement because the provider has a two-week change process. Requesting a full table and filtering inbound would provide flexibility but wastes memory and CPU on the customer router because all routes are still received before filtering. A maximum-prefix limit does not select the correct routes. ORF is therefore the scalable operational design for receiving a default route and selected prefixes with minimal provider involvement. Reference topics: BGP ORF, prefix-based filtering, inbound route control, ISP peering design, routing table scale.