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

The multicast-replicator function is used to optimize multicast traffic distribution across Cisco SD-WAN. Cisco Catalyst SD-WAN multicast overlay design avoids forcing the ingress WAN Edge router to replicate every multicast packet to every remote receiver. Instead, multicast routes and receiver information are exchanged through OMP, and a WAN Edge can be designated as a multicast or OMP replicator. The replicator then distributes streams to interested receivers across the overlay, reducing bandwidth and processing pressure on the source-side edge. That is why multicast-replicator is the feature that optimizes WAN bandwidth for IGMP-driven multicast receiver traffic among WAN Edge routers in the same VPN. IGMPv2 is only the host-to-router group membership protocol and does not optimize overlay distribution by itself. A multicast RP is used in PIM sparse mode, but it is not the SD-WAN overlay replication feature. Multicast service routes advertise multicast service information, but the bandwidth-saving forwarding role is the replicator. Reference topics: Cisco SD-WAN multicast overlay, OMP multicast routes, multicast replicator, IGMP receiver joins.

The correct overlay considerations are that virtual networks provide data-plane isolation and that overlapping IP addresses should be avoided for operational simplicity. In Cisco SD-Access, virtual networks are used for macro segmentation and are commonly mapped to VRFs. This separates routing and forwarding tables between major groups such as corporate users, guests, IoT, and shared services. Security Group Tags provide finer policy control and microsegmentation, but they are not the primary mechanism for data-plane isolation between virtual networks. The phrase “virtual networks should be used for microsegmentation” is therefore inaccurate; microsegmentation is SGT and SGACL driven. Although overlapping IP addresses can technically exist in separate VRF-like contexts, Cisco design practice discourages unnecessary overlap because it complicates troubleshooting, service insertion, external connectivity, and inter-VN communication. A clean overlay address plan improves operations and reduces policy ambiguity. Reference topics: SD-Access overlay design, virtual networks, macro segmentation, SGTs, microsegmentation, overlapping IP avoidance. This also simplifies day-two operations.

The Cisco SD-Access data plane is based on VXLAN. Cisco SD-Access separates the fabric into functional planes: the underlay provides IP reachability, the control plane uses LISP to map endpoints to locations, and the data plane uses VXLAN encapsulation to carry user traffic across the routed underlay. VXLAN allows the fabric edge node to encapsulate endpoint traffic and forward it through the fabric while preserving virtual network and segmentation information. This is what enables SD-Access to provide Layer 2 and Layer 3 overlay services over a Layer 3 routed transport. OMP is the control-plane protocol for Cisco SD-WAN, not SD-Access. NHRP is associated with DMVPN tunnel resolution. LISP is essential in SD-Access, but its role is endpoint ID to routing locator mapping, not packet encapsulation in the data plane. Therefore, VXLAN is the correct protocol for the SD-Access data plane. Reference topics: SD-Access fabric, VXLAN data plane, LISP control plane, overlay encapsulation, routed underlay.