Implementing Zero Trust with SGT-Based Micro-Segmentation: ISE + TrustSec from 802.1X to SGACL

Zero trust gets thrown around constantly, but Cisco TrustSec is one of the few frameworks that translates the concept into actual switch configurations. ISE combined with TrustSec uses Scalable Group Tags (SGTs) — 16-bit labels assigned during authentication — to enforce identity-based access policies across your entire infrastructure, replacing thousands of IP-based ACLs with a centralized policy matrix. Here's how the full architecture works, end to end — with real configs, scalability limits, and the deployment pain points the docs don't mention. How TrustSec SGT Segmentation Actually Works Step 1: Authentication (802.1X / MAB) Everything starts with identity. When an endpoint connects to a Catalyst switch port, it authenticates via: 802.1X — supplicant-based (Windows, macOS, Linux machines with a certificate or EAP credentials) MAB (MAC Authentication Bypass) — for devices that can't run a supplicant (IP phones, printers, IoT sensors) The switch sends the authentication request to