According to Juniper Mist documentation regarding campus fabric design, the campus fabric IP Clos (also known as a 5-stage Clos) is the architecture that extends the EVPN-VXLAN protocol stack from the core tier down through the distribution tier and finally to the access tier. In this model, every switch in the hierarchy- from the high-capacity core switches to the wiring closet access switches-participates in the EVPN control plane and VXLAN data plane.
By extending EVPN-VXLAN to the access tier, the IP Clos architecture provides a standards-based, scalable framework that allows for seamless Layer 2 connectivity over a Layer 3 underlay across the entire campus333333333. This enables advanced features like Microsegmentation using Group-Based Policies (GBP) and Macrosegmentation via Virtual Routing and Forwarding (VRF) instances directly at the edge of the network.
In contrast, other architectures like "core-distribution" (either CRB or ERB) typically limit the EVPN- VXLAN fabric to the core and distribution layers, leaving the access tier to connect via traditional methods like LAG, Virtual Chassis, or standard Layer 2 trunks5555. The IP Clos architecture is specifically designed for large-scale deployments where high density, vendor interoperability, and end-to-end policy enforcement are critical6. By utilizing a 5-stage IP Clos, organizations can eliminate the complexities of Spanning Tree Protocol (STP) while maintaining a flexible, "any-to-any" communication path throughout the physical infrastructure.

Juniper's officialCampus Fabric IP Clos designfor Mist Wired Assurance defines that the3-stage IP Clostopology eliminates the traditionaldistribution layerentirely. This architecture is intended for smaller campus environments that do not need an intermediate distribution layer between the access and core.
"Juniper's Wired Assurance supports 3-Stage and 5-Stage IP Clos deployments. The 3-Stage IP Clos is targeted towards deployments that do not require a Distribution Layer and have smaller scale requirements." Because the distribution layer is not present, the only hierarchical connection in a 3-stage campus fabric is between thecore and access layers. Traffic is routed directly at the access layer, and each access switch acts as a Layer-3 gateway (IRB) for its VLANs.
"In a campus fabric IP Clos architecture, Mist provisions Layer-3 (L3) integrated routing and bridging (IRB) interfaces on the access layer. All the access switches are configured with the same IP address for each L3 subnet." Additionally, the Juniper documentation explains that point-to-point links are configuredbetween layers, and in the case of the 3-stage design (with no distribution), this means between thecore and accessdevices:
"The point-to-point links between each layer utilize /31 addressing to conserve addresses." Therefore, the correct statement isC: The core layer is connected to the access layer.
OptionsAandBincorrectly mention a distribution layer that does not exist in this topology.
OptionDis incorrect because core (spine) devices in a Clos fabric are not interconnected with each other.
References:
Juniper Mist AI for Wired - Campus Fabric IP Clos Architecture Guide
Juniper Mist AI for Wired - Campus Fabric IP Clos Workflow
Juniper Mist AI for Wired - Configure Campus Fabric IP Clos
Juniper Validated Design - Campus Fabric IP Clos Deployment Types