You are using a single tenant data center with a bridged overlay architecture.

Understanding Bridged Overlay Architecture:

In a single-tenant data center using a bridged overlay architecture, virtual networks (VLANs) are typically isolated within the fabric, with traffic between these VLANs handled outside the fabric.

Communication Between Different Virtual Networks:

A. off-fabric using an external device:This is correct. In many bridged overlay architectures, communication between different virtual networks is handled off-fabric, often using an external router or firewall that connects the different VLANs. The fabric itself primarily provides Layer 2 connectivity within each VLAN, leaving inter-VLAN routing to be handled externally.

Data Center References:

This design is common in smaller or simpler data center environments where a single tenant does not require complex on-fabric routing and prefers to handle inter-VLAN routing through dedicated devices.