In SD-Access, the overlay network provides logical segmentation (virtual networks) over a common underlay. Using overlapping IP subnets across multiple virtual networks can create routing and interoperability complexity, especially when inter-VN communications or shared services are required, which increases operational burden. Therefore, avoiding overlapping IP address spaces across overlay networks simplifies provisioning, routing, and troubleshooting.
This aligns with standard SD-Access guidance that encourages distinct address spaces per virtual network to maintain clear separation and predictable behavior.
Scalable Group Tags (SGTs) are Cisco TrustSec mechanisms used to implement policy-based segmentation and microsegmentation within and across virtual networks. They enable data-plane isolation and fine-grained access control between devices based on their SGT, supporting constraint-based communication even within the same virtual network. This is a core capability of SD-Access for enforcing segmentation policies at the data plane.