Network Segmentation — VLANs, VRFs, Microsegmentation, and the Tiers Auditors Actually Look For

Manish Garg
Manish Garg Associate of (ISC)² · RingSafe
Apr 27, 2026
11 min read
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Last updated: May 1, 2026

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Segmentation is splitting your network into zones with controlled traffic between them. Done well it slows lateral movement, reduces blast radius, and is the single control RBI/SEBI/IRDAI auditors quote most often. This module covers VLAN segmentation (the campus baseline), VRF for L3 separation, microsegmentation (host-based / cloud-native security groups), the tier model defenders rely on, and the practical “where do I put what” guide.

Segmentation is the difference between “one foothold leads to domain compromise” and “one foothold leads to one VLAN compromise.” Almost every Indian breach in the last three years that escalated to domain admin would have been contained by competent segmentation. This module is the practitioner introduction: VLANs at L2, VRFs at L3, microsegmentation per host or workload, and the trust-tier model that maps controls to business risk.

Why segmentation is the single highest-leverage control

When attackers land an initial foothold (phished employee laptop, vulnerable web app), their first step is lateral movement: scan the local subnet, find a domain controller or file server, escalate. A flat network turns one compromised host into total compromise. Segmentation forces the attacker to traverse choke points — and choke points are where your IDS, EDR, and access controls live. Auditors love segmentation because it is observable: show me the network diagram, show me the firewall rules between zones, show me the segment-bridging device logs. RBI Cyber Security Framework Annex 1 and SEBI CSCRF both call out segmentation explicitly.

Practical baselineat minimum separate user / server / management / DMZ / IoT into distinct broadcast domains with explicit inter-segment ACLs.

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