Tier 0 / Tier 1 Enterprise Architecture Standard
Tier 0 / Tier 1 Enterprise Architecture Standard
Zero Trust Control Plane Model
Executive Summary
The enterprise operates under a Zero Trust control plane architecture
in which no user, device, or system is inherently trusted at any point.
Instead of static trust boundaries, the environment is governed by a continuous
verification model that evaluates identity, device posture, risk signals,
and network state before and during every access request.
This model is built on a simple principle:
Trust is never granted. It is continuously evaluated, enforced, and
revalidated in real time.
Zero Trust Design Principles
All infrastructure services operate under a unified set of principles:
- Verify explicitly for every
access request
- Enforce least privilege at all
times
- Assume breach as the default
security posture
- Continuously evaluate trust
throughout sessions
- Apply context-aware policy
enforcement dynamically
These principles define how every system in the enterprise must behave,
not just how it is configured.
Tier 0 Control Plane
Identity & Security Authority
Layer
Tier 0 defines the foundation of enterprise trust. It establishes
identity, cryptographic assurance, and privileged access boundaries that all
other systems depend on.
Nothing in the environment is considered secure without first passing
through Tier 0 trust validation.
Active Directory (Identity Authority)
Active Directory is the authoritative identity system for the enterprise
and serves as the root of all authentication decisions.
It defines who a user is, but it does not alone define whether
they are trusted at any given moment.
All identity-based decisions are subject to downstream validation through
the Zero Trust enforcement layers.
Key behaviors:
- Identity is authoritative but not
sufficient for access
- Authentication is always
contextually evaluated
- No external system overrides
identity state
Privileged Access Model
Privileged access is treated as a controlled security event rather than a
standing permission.
Administrative activity is explicitly separated from standard user
activity and is continuously validated through policy enforcement.
Key behaviors:
- Privilege is time-bound and
session-based
- No persistent administrative
trust is allowed
- All privileged actions are fully
auditable and monitored
PKI (Cryptographic Trust Anchor)
PKI establishes cryptographic identity for systems, services, and users.
However, certificates represent identity assurance—not implicit trust.
Key behaviors:
- Certificate issuance is centrally
governed
- Trust is validated at time of use
- Certificate lifecycle is
continuously enforced and audited
Identity Enforcement Layer
MFA + Conditional Access + Device
Trust
This layer enforces real-time trust validation on top of Tier 0
identity systems. It determines whether an authenticated identity is permitted
to proceed based on context, device posture, and risk.
Multi-Factor Authentication (MFA)
MFA provides the first layer of explicit identity verification beyond
credentials.
It ensures that identity alone is never sufficient for access.
Key behaviors:
- Required for all privileged and
sensitive access
- Strong authentication is enforced
proportionally to risk
- Authentication events are
continuously logged and monitored
Conditional Access (Entra ID)
Conditional Access acts as the real-time policy decision engine for all
access attempts.
It evaluates multiple signals simultaneously to determine whether access
is allowed.
Evaluated signals include:
- Identity and group membership
- MFA strength and completion
- Device compliance posture
- Sign-in and user risk levels
- Geographic and behavioral context
Key behaviors:
- Access decisions are made per
session, not per user
- Trust is dynamically evaluated at
sign-in and during use
- High-risk conditions trigger
step-up or block actions
Intune Device Compliance
Device compliance determines whether a device is trusted to participate
in enterprise access.
Devices are never assumed to be trusted by default.
Key behaviors:
- Devices must meet security
baseline requirements
- Compliance is continuously
evaluated, not static
- Unmanaged devices are considered
untrusted by default
Compliance requirements include:
- Supported and patched operating
system
- Disk encryption enabled
- Endpoint protection active
- Secure configuration baseline
enforced
Unified Identity Access Flow
All access requests follow a consistent evaluation chain:
Identity → MFA → Device Compliance → Conditional Access → Risk Evaluation
→ Session Authorization
Only after passing all layers is access granted.
Tier 1 Control Plane
Core Network Services &
Connectivity Layer
Tier 1 defines how systems communicate, how they are addressed, and how
network state is maintained across the enterprise.
It operates as a tightly integrated control plane rather than a
collection of independent services.
Core Network Services (Unified Model)
Core Network Services consist of:
- IP Address Management (IPAM)
- DHCP
- DNS
These systems operate as a single coordinated control system responsible
for network structure, addressing, and name resolution.
Network Control Model
The relationship between services is strictly defined:
- IPAM defines the intended network
structure
- DHCP executes dynamic address
assignment within that structure
- DNS provides validated name
resolution for assigned identities
This creates a closed-loop system where all network state is continuously
aligned.
IPAM (Network Authority Layer)
IPAM is the authoritative system for all network structure and
addressing.
It defines what the network should be—not what it temporarily becomes.
Key behaviors:
- All subnets and pools originate
in IPAM
- No unmanaged IP space is
permitted
- DHCP and DNS derive configuration
from IPAM
IPAM changes represent intentional modifications to enterprise network
design and must be strictly controlled.
DHCP (Controlled Execution Layer)
DHCP operates strictly within IPAM-defined boundaries and is responsible
for dynamic IP allocation.
It does not define network structure—it enforces it.
Key behaviors:
- All scopes are derived from IPAM
- Address allocation is strictly
bounded and controlled
- Rogue or unauthorized DHCP
activity is treated as a security incident
- High availability and failover
are mandatory
DNS (Resolution Trust Layer)
DNS provides authoritative name resolution across the enterprise.
It reflects validated network state rather than acting as an independent
source of truth.
Key behaviors:
- DNS records must reflect verified
system state
- Dynamic updates are securely
controlled
- Orphaned or inconsistent records
are treated as anomalies
- Full query and change logging is
required
Network Integrity Model
The Core Network Services operate as a continuous validation loop:
- IPAM defines structure
- DHCP assigns addresses
- DNS resolves identities
- Systems reconcile and validate
state
Any deviation between these systems is treated as a critical
infrastructure integrity failure requiring immediate correction.
Network Access Control Layer
Network Policy Server (NPS)
NPS enforces network access decisions based on validated identity and
policy context.
Network access is never implicitly trusted based on location or
connectivity.
Key behaviors:
- Identity must be validated before
network access is granted
- MFA and Conditional Access
signals influence network decisions
- Access policies are centrally
enforced and audited
- No bypass paths are permitted
outside controlled exception processes
Administrative Control Model
Privileged Access Enforcement Layer
Administrative access is treated as a high-risk, continuously monitored
activity class.
Key behaviors:
- Privileged access is
session-based and time-limited
- No persistent administrative
trust exists
- All administrative actions are
fully logged and traceable
- Privileged Access Workstations
are required for sensitive operations
Access is continuously evaluated, not permanently granted.
Monitoring, Logging &
Continuous Validation
Monitoring systems operate as active validation engines rather than
passive logging platforms.
They continuously assess whether the environment is operating within
defined trust boundaries.
Key coverage areas:
- Identity and authentication
events (AD / Entra ID / MFA)
- Device posture and compliance
state (Intune)
- Network state (IPAM / DHCP / DNS)
- Access decisions (Conditional
Access / NPS)
- Security anomalies and drift
conditions
Any deviation from expected state is treated as a security signal, not a
technical anomaly.
Change Management Control Plane
All infrastructure changes are treated as modifications to the enterprise
trust model.
Changes must follow a controlled, validated workflow.
Standard flow:
IPAM → DHCP → DNS → Validation → Monitoring
Key behaviors:
- All changes require formal
approval
- Emergency changes must be
reconciled post-implementation
- No direct-to-production
modifications outside break-glass processes
- Cross-system validation is
mandatory
Zero Trust Integrity Statement
The enterprise is built on a fundamental assumption:
- No user is inherently trusted
- No device is inherently trusted
- No network location is inherently
trusted
- No session remains trusted
without continuous validation
Trust is not a static state—it is a continuously evaluated condition.
Unified Architecture Summary
The enterprise operates as a layered Zero Trust control plane:
Tier 0 Control Plane
Identity, PKI, and privileged access governance
⬇️
Identity Enforcement Layer
MFA, Conditional Access, and device compliance (Entra ID / Intune)
⬇️
Tier 1 Control Plane
DNS, DHCP, and IPAM network services
⬇️
Network Access Control Layer
NPS and network policy enforcement
⬇️
Continuous Monitoring Layer
SIEM, drift detection, compliance validation, and behavioral analytics
Final Statement
This architecture implements a modern Zero Trust enterprise model in
which:
- Identity is continuously verified
- Devices are continuously
validated
- Network state is continuously
reconciled
- Access is continuously evaluated
The result is an environment where trust is never assumed—only
continuously proven.
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