In an EVPN-VXLAN edge-routed bridging (ERB) architecture, the Layer 3 gateway functionality is distributed to the edge devices (leaf or distribution switches). This model uses a distributed anycast gateway, where all participating leaf switches are configured with the same IP address and MAC address on their Integrated Routing and Bridging (IRB) interfaces for a given VLAN. This allows end hosts to use a consistent default gateway regardless of which leaf switch they are connected to, enabling optimal east-west traffic routing directly at the distribution layer.

A. Using unique IP addresses on each switch for the gateway is inefficient and characteristic of legacy designs using protocols like VRRP, which the EVPN anycast gateway model replaces.

C. This describes a centrally-routed bridging (CRB) model, where Layer 3 routing is handled by core or spine devices, not an edge-routed design.

D. IRB interfaces are fundamental to the ERB model as they provide the Layer 3 routing capability at the edge; they must be enabled and configured.

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1. Juniper Networks TechLibrary, Data Center Fabric Architecture and Design Guide. In the "Edge-Routed Bridging Overlay" section, it states, "In an ERB overlay, the leaf devices function as both Layer 2 and Layer 3 gateways... To enable a host to move from one leaf device to another in the same VLAN and maintain its existing default gateway IP address, you can configure all leaf devices with the same IP address for the IRB interface... This feature is known as a default gateway or anycast gateway." (Reference: Data Center Fabric Architecture and Design Guide, Chapter: EVPN-VXLAN Fabric Architectures, Section: Edge-Routed Bridging Overlay).

2. Juniper Networks TechLibrary, EVPN-VXLAN Campus Architecture Guide. In the section "Edge-Routed Bridging Overlay Design," it explains, "In an ERB overlay, the access switches function as Layer 2 and Layer 3 gateways... All of the access switches in the EVPN-VXLAN fabric are configured with the same virtual gateway IP address and MAC address, which enables any of the access switches to act as the default gateway." (Reference: EVPN-VXLAN Campus Architecture Guide, Section: Edge-Routed Bridging Overlay Design).

3. Juniper Networks TechLibrary, Understanding EVPN with VXLAN Data Plane Encapsulation. Under the section "Symmetric and Asymmetric Integrated Routing and Bridging," the symmetric IRB model (which corresponds to ERB) is described as having IRB interfaces on all VTEPs (leaf switches) that need to perform routing. It highlights the use of a common gateway IP address across these VTEPs. (Reference: Junos OS EVPN User Guide, Section: Understanding EVPN with VXLAN Data Plane Encapsulation).