172.20.0.128/25 for Customer A supports 128 IPs (126 usable), which fits 125 hosts.
172.20.1.0/26 for Customer D supports 64 IPs (62 usable), which fits 62 hosts.
/30 subnets (172.20.1.68/30, 172.20.1.72/30, 172.20.1.76/30) provide 4 IPs each (2 usable), ideal for point-to-point links, maximizing subnet usage and minimizing waste.

BIDIR-PIM is the correct multicast deployment model when redundant paths and active links may create RPF challenges for many-to-many multicast traffic. Bidirectional PIM builds a shared tree rooted at the rendezvous point and avoids maintaining separate source-specific shortest-path trees for every sender. This is valuable when sources and receivers are spread across a redundant branch design and traffic can enter the multicast domain from multiple directions. Because BIDIR-PIM uses the Designated Forwarder mechanism on each link, it helps control which router forwards traffic toward the RP and reduces duplicate forwarding in topologies where normal RPF behavior could be problematic. PIM-SM is widely used, but it normally moves to source trees for active sources unless specifically controlled. PIM-SSM requires receivers to know the source and is not designed for arbitrary many-to-many communication. PIM-BSR is a mechanism for dynamic RP discovery, not a multicast forwarding model. Reference topics: BIDIR-PIM, multicast RPF, many-to-many multicast, Designated Forwarder, branch multicast design.

The validated answer is Option D because this item depends on the exhibit containing configuration or model fragments. In Cisco programmability questions, the correct option is determined by whether the selected YANG or API payload accurately represents the intended configuration hierarchy, data types, and device- specific path. The answer must match the complete model structure, not merely contain the right-looking address, interface name, or protocol value. Option D should therefore be retained as the verified selection because it is the only option that aligns with the expected data model structure shown in the exhibit. For these items, the professional review must avoid inventing a replacement payload when the answer choices are embedded as images. The proper explanation is that YANG-based configuration validation requires the namespace, container path, list keys, and leaf values to match the model used by the target platform.
Reference topics: YANG configuration validation, RESTCONF or NETCONF payload structure, model hierarchy, Cisco IOS XE programmability, exhibit-based option verification.

Endpoint registration-Each edge node has a LISP control-plane session to all control plane nodes. After an endpoint is detected by the edge node, it is added to a local database called the EID-table. Once the host is added to this local database, the edge node also issues a LISP map- register message to inform the control plane node of the endpoint so the central HTDB is updated.
https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Campus/cisco-sda-design-guide.html

The most efficient campus design aligns the active first-hop gateway with the Layer 2 forwarding path. In a traditional access-distribution topology using STP and HSRP, traffic should not cross the distribution-to- distribution link simply because the HSRP active gateway is on the opposite distribution switch from the STP forwarding path. Cisco campus design guidance stresses aligning the STP root bridge with the active FHRP gateway so hosts forward northbound traffic directly to the distribution switch that owns the optimal Layer 2 path. Reconfiguring distribution switch A to become the HSRP active device fixes the asymmetric and inefficient traffic flow in the exhibit. Adding a link between access switches would extend the Layer 2 domain and increase loop-prevention complexity, not improve the northbound default-gateway path. Changing the distribution interconnect to a routed link may be valid in a routed-access redesign, but it is not the targeted correction for this Layer 2/FHRP misalignment. An EtherChannel between distribution switches only increases interswitch capacity; it does not remove the unnecessary hairpin path caused by the wrong active gateway.