Network Security: Segmentation & NAC Best Practices 

Introduction: Securing the Modern Campus

The contemporary campus network is a dynamic and complex environment. It must seamlessly support a diverse mix of users (employees, students, guests, contractors), an explosion of device types (corporate-owned, BYOD, IoT, OT), and critical applications hosted on-premises and across multiple cloud platforms. This inherent complexity creates a significant attack surface and necessitates robust security measures that extend far beyond traditional perimeter defenses. The inadequacy of the traditional "castle-and-moat" security model, focused solely on the network perimeter, is evident in today's landscape. Threats can easily originate from within (insider threats, compromised devices) or bypass the perimeter entirely via BYOD or IoT devices. Once an attacker gains internal access on a flat, unsegmented network, they can often move laterally with minimal resistance.

Foundational strategies for securing the modern campus involve comprehensive LAN segmentation and robust Network Access Control (NAC). Segmentation divides the network into isolated zones to contain threats and enforce policy, while NAC acts as a vigilant gatekeeper, verifying identities and device health before granting access. However, traditional approaches often struggle with the scale and complexity of modern demands. Leading NAC solutions like Cisco Identity Services Engine (ISE), and Arista Guardian for Network Identity (AGNI) offer different architectures and capabilities to address these challenges.

What you'll find on this page:

LAN Segmentation Techniques

To overcome the limitations of traditional segmentation, particularly VLAN scalability, modern campus architectures increasingly adopt overlay technologies like Virtual Extensible LAN (VXLAN) with Ethernet VPN (EVPN) as the control plane, a standard supported by Arista's Cognitive Campus portfolio.

Concept: VXLAN encapsulates Layer 2 Ethernet frames within UDP packets, allowing L2 segments to extend across an underlying Layer 3 network. EVPN serves as the standards-based control plane, efficiently distributing MAC and IP address reachability information.

Benefits in Campus:

Scalability: VXLAN uses a 24-bit Virtual Network Identifier (VNI), allowing for ~16.7 million segments, vastly exceeding the 4094 VLAN limit, crucial for accommodating device proliferation.

Flexibility: Decouples the logical overlay from the physical underlay, allowing segments (VNIs) to span the L3 fabric irrespective of physical location or subnet boundaries, simplifying modern leaf-spine architectures.

Cognitive Campus Alignment: Supports Arista's vision for an automated, telemetry-driven, and operationally simple campus network.

Deployment: Arista supports VXLAN/EVPN in various campus fabric designs (L2, L3, L2/L3).13 Configuration can be streamlined via Arista CloudVision. Gateways can be distributed or centralized. This approach addresses the scalability and flexibility limits of traditional designs.

Advanced Policy-Based & Micro-segmentation Techniques

Micro-segmentation: This advanced technique provides highly granular segmentation, often down to the individual workload, application, or even process level. It typically uses software-defined approaches (like host-based firewalls or overlay network policies) to create secure zones independent of the underlying network topology. Policies are often enforced at Layer 4-7. Micro-segmentation is extremely effective at preventing lateral movement and is a core component of Zero Trust strategies.

Policy-Based Segmentation (Dynamic Segmentation): Instead of static port/subnet assignments, devices or users are dynamically placed into segments based on attributes like identity, role, device type, location, or security posture. This is often orchestrated by NAC systems (like Arista AGNI 2, Cisco ISE, or Aruba ClearPass) or Software-Defined Networking (SDN) controllers using mechanisms like downloadable ACLs (dACLs), dynamic VLAN assignment, or security group tags (e.g., Cisco TrustSec Security Group Tags (SGTs)). This approach offers greater flexibility and automation compared to static segmentation.

Arista MSS (Multi-Domain Segmentation Service): Arista MSS provides a sophisticated framework for defining and enforcing granular security policies between and within network segments, moving towards identity-based control.2 It complements traditional firewalls by extending security deep into the network.

MSS-Group: Classifies endpoints (users, devices, IoT) into logical "groups" independent of IP address, subnet, or VLAN.1 CloudVision dynamically discovers group memberships by integrating with sources like Arista AGNI, VMware vCenter, ServiceNow, IPAM, other NACs (Forescout, Cisco ISE), or static definitions.

Policy Definition: Security policies (allow/deny) are created between these logical groups, simplifying management compared to IP-based ACLs.

Distributed Enforcement: Policies defined in CloudVision are translated into hardware-enforced rules on Arista EOS switches using efficient, locally significant MSS tags, ensuring wire-speed enforcement without performance impact. MSS addresses the operational burden of complex VLANs/ACLs through abstraction and automation.

MSS Firewall Service Insertion: MSS can dynamically redirect specific inter-group traffic to security devices (e.g., Palo Alto Networks, Check Point, Fortinet firewalls) for deeper inspection, automated via CloudVision.

Management: The entire MSS framework is orchestrated and managed centrally through Arista CloudVision using dedicated tools (MSS Studio, Policy Manager, etc.) for group definition, policy building, deployment, and monitoring.

The choice of segmentation technique depends on specific security requirements, network complexity, budget, and operational capabilities. Often, a combination of techniques (e.g., VLANs/subnetting for broad segmentation, firewalls for inter-segment control, VXLAN for scale, MSS or TrustSec for granular policy and micro-segmentation) provides the most effective layered security.

Table: Comparison of LAN Segmentation Techniques

Security Benefits of Segmentation

Implementing network segmentation yields significant security advantages, amplified by modern approaches:

Reduced Attack Surface: By dividing the network, segmentation limits the visibility and accessibility of assets. Using numerous VXLAN VNIs or fine-grained Arista MSS groups or Cisco TrustSec SGTs makes discovery and exploitation more difficult.

Improved Breach Containment (Limiting Lateral Movement): This is perhaps the most critical benefit. Segmentation acts like a bulkhead, preventing threats from spreading horizontally. Arista MSS excels here, enabling identity-based micro-segmentation to create granular internal boundaries (microperimeters) that effectively contain threats even within the same subnet or VLAN, offering superior containment compared to VLANs alone. Similarly, Cisco TrustSec uses SGTs enforced by network devices to achieve granular segmentation.

Enhanced Data Security: Sensitive data can be isolated within highly secured segments (VNIs, MSS groups, or SGT-based zones) with strict ingress/egress controls enforced by segmentation policies or integrated firewalls, minimizing unauthorized access risk.

Better Access Control (Least Privilege): Segmentation facilitates enforcing the principle of least privilege. Arista MSS-Group policies, based on verified identity (often from AGNI), allow precise definition of inter-group communication. Cisco ISE and Aruba ClearPass similarly enable policies based on user roles, device types, and posture, assigning appropriate VLANs, dACLs, or SGTs to grant only necessary access.

Improved Monitoring and Threat Detection: Monitoring traffic between well-defined segments is simpler and more effective. Anomalous communication attempts, especially those denied by segmentation policies (MSS, SGTs, ACLs), are easier to detect. Integrating logs from NAC (AGNI, ISE, ClearPass) and segmentation enforcement points into SIEM provides richer context.

Simplified Compliance: Segmentation helps meet regulatory mandates (PCI DSS, HIPAA, GDPR) by isolating scoped systems/data. Arista MSS-Group or Cisco TrustSec can create specific segments for regulated data, applying strict policies and demonstrably reducing audit scope and cost.

Zero Trust Alignment

Effective network segmentation, particularly the granular, identity-aware control offered by solutions like Arista MSS or Cisco TrustSec (orchestrated by ISE), serves as a cornerstone for implementing a Zero Trust security model. Zero Trust operates on "never trust, always verify" and least privilege, demanding precise control over all communications. Segmentation, especially micro-segmentation, provides the necessary architectural foundation by creating isolated zones (microperimeters) and policy enforcement points for granular, identity-aware Zero Trust policies. Attempting Zero Trust on a flat network is impractical. The ability of modern NAC and segmentation solutions to contain breaches and enforce least privilege based on identity directly fulfills core Zero Trust requirements.

Deploying Network Access Control (NAC)

Network Access Control (NAC) solutions provide a mechanism to enforce security policies for devices and users attempting to connect to the network. NAC goes beyond simple authentication; it typically assesses device health (posture), considers user identity and role, and applies granular access policies based on this context before and sometimes during the network session. Implementing NAC is a significant project requiring careful planning and execution, involving solutions like Cisco ISE, Aruba ClearPass, and Arista AGNI.

Leading NAC Solutions Overview

Cisco Identity Services Engine (ISE): A comprehensive policy control platform providing AAA, posture, profiling, guest management, and BYOD onboarding. ISE is often deployed as physical appliances (SNS series 38) or virtual machines 39 and typically uses a distributed architecture with distinct personas: Policy Administration Node (PAN), Policy Service Node (PSN), and Monitoring & Troubleshooting Node (MnT). Deployment models range from standalone (lab/PoC) to small, medium, and large distributed setups to handle varying scale and redundancy requirements. ISE is known for deep integration with Cisco network infrastructure and security ecosystem via pxGrid and TrustSec.

Aruba ClearPass Policy Manager: A role- and device-based NAC solution supporting multi-vendor wired, wireless, and VPN infrastructures. ClearPass can be deployed as hardware appliances (C-series 48) or virtual appliances on platforms like VMware ESXi and Microsoft Hyper-V. It utilizes a cluster architecture with a Publisher/Subscriber model for scalability and high availability, where the Publisher manages configuration and replicates it to Subscribers. ClearPass is recognized for its vendor neutrality and extensive third-party integration capabilities via ClearPass Exchange. User feedback often highlights its intuitive user interface compared to ISE.

Arista Guardian for Network Identity (AGNI): Arista's next-generation, cloud-native NAC solution designed for modern enterprise complexities. Built on cloud principles and AI/ML, AGNI simplifies deployment, management, and security.2
Cloud-Native SaaS Model: AGNI is primarily a cloud-delivered SaaS offering (though on-prem exists 2), eliminating the burden of managing on-prem appliances. This reduces hardware, simplifies installation (hours vs. weeks), provides automatic updates, and ensures high availability.

Scalability: Built on containerized microservices (Kubernetes), AGNI scales elastically from hundreds to millions of users/devices without complex capacity planning.

Simplified Management: Managed via Arista CloudVision, AGNI offers a single pane of glass for configuration, monitoring, and policy. AI/ML capabilities, potentially including the AVA conversational interface, further simplify tasks. AGNI addresses the historical complexity of traditional NAC, lowering TCO and operational friction.

Deployment Steps (Considering Major NAC Solutions)

Assessment and Planning:

Define clear objectives: (e.g., BYOD security, IoT visibility, compliance, guest access control, Zero Trust enablement).

Inventory network assets: Identify all connecting devices (corporate, BYOD, IoT, guest, contractor).

Assess current infrastructure: Evaluate switch/AP capabilities (802.1X support), existing identity sources (e.g., Active Directory, LDAP, cloud IDPs like Azure AD, Okta, Google Workspace that AGNI, ISE, and ClearPass integrate with), and security posture.

Define scope: Determine where NAC will be implemented (e.g., wired, wireless, specific buildings, entire campus).

Solution Selection:

Evaluate features: Compare vendor offerings (ISE, ClearPass, AGNI) based on required capabilities: deployment model (appliance, VM, cloud), device profiling, posture assessment, authentication methods, guest portals, reporting, vendor integration (e.g., Cisco integration for ISE, multi-vendor for ClearPass, Arista integration for AGNI), and management interface usability.

Consider architecture: Pre-admission vs. post-admission checks. Deployment model (on-premises, VM, Cloud [AGNI primary model]).

Scalability and compatibility: Ensure the solution handles current/future load and integrates with existing systems.

Policy Definition:

Develop granular policies using the chosen NAC's context: Who (user role/IDP group)? What (device type/profile, posture via EDR/MDM)? Where (network location/VLAN/SGT/MSS-Group)? When (time)? How (connection type)?

Apply least privilege.

Define outcomes: Grant full access, assign to VLAN/SGT/MSS-Group, grant limited/guest access, quarantine, block.

Infrastructure Preparation:

Configure network devices: Enable 802.1X/MAB on switch ports/SSIDs. Configure RADIUS settings pointing to the NAC servers (ISE PSNs, ClearPass Cluster, AGNI Service). For AGNI, configure RadSec (RADIUS over TLS) for secure AAA communication.

Integrate identity sources: Connect the chosen NAC to AD or cloud IDPs.

Pilot Testing & Onboarding Strategy:

Start small: Deploy in a limited, controlled environment (monitor-only mode initially is an option).

Plan onboarding: Consider self-service portals (ISE 33, ClearPass Onboard 35, AGNI 2) for BYOD certificate/key provisioning.

Test thoroughly: Validate authentication (802.1X, MAB, other methods), posture checks, policy enforcement (VLAN/dACL/SGT/MSS-Group assignment), guest access, and remediation.

Phased Rollout:

Expand gradually across areas or user groups.

Communicate and support: Inform users, provide instructions, ensure helpdesk readiness.

Ongoing Monitoring and Optimization:

Monitor logs and performance via the NAC's console (ISE MnT, ClearPass Insight, CloudVision for AGNI).

Refine policies based on experience, feedback, and evolving requirements.

Audit regularly.

Implementing NAC, regardless of the chosen solution, is an ongoing process requiring continuous vigilance and adaptation.

NAC Authentication Methods: 802.1X vs. MAB and Vendor Enhancements

Network Access Control fundamentally relies on authenticating users or devices before granting network access. While traditional methods like IEEE 802.1X and MAC Authentication Bypass (MAB) remain relevant, leading NAC solutions like Cisco ISE, Aruba ClearPass, and Arista AGNI offer enhanced capabilities and more secure alternatives.

Traditional Methods Supported by Major NACs

IEEE 802.1X: This standard provides a robust framework for port-based authentication involving a Supplicant (client device), Authenticator (switch/AP), and Authentication Server (RADIUS server like ISE PSN, ClearPass, or AGNI). It uses the Extensible Authentication Protocol (EAP) for credential exchange. Various EAP methods exist (e.g., EAP-TLS using certificates, PEAP/EAP-TTLS using passwords). 802.1X enables dynamic policy assignment (VLANs, ACLs, Security Groups) and is considered highly secure but requires client-side supplicant support. All three major NACs fully support 802.1X.

MAC Authentication Bypass (MAB): MAB serves as an alternative for devices unable to perform 802.1X (printers, cameras, simple IoT, legacy systems). The authenticator uses the device's MAC address as its identifier , sending it to the RADIUS server (ISE, ClearPass, AGNI) for validation against a known database.36 If authorized, access (potentially with VLAN/policy assignment) is granted. MAB is simpler for non-802.1X devices but significantly weaker due to MAC spoofing vulnerability. It's often used as a fallback. All three major NACs support MAB.

Vendor-Specific Authentication Enhancements

Cisco ISE: While primarily relying on standard 802.1X and MAB, ISE excels in integrating authentication outcomes with Cisco TrustSec to assign Security Group Tags (SGTs) for policy enforcement within the fabric. It also offers robust certificate management capabilities, often integrating with enterprise PKI.

Aruba ClearPass: ClearPass supports standard 802.1X and MAB, but also offers flexible web-based authentication (captive portal) workflows for guest and BYOD onboarding. It supports multi-factor authentication (MFA) triggered based on context and integrates with various token servers. The ClearPass Onboard module provides automated provisioning and certificate management for BYOD devices.

Arista AGNI: AGNI builds upon standards with enhanced options:

802.1X with Robust PKI: AGNI strongly advocates certificate-based EAP-TLS 4 and features a built-in Public Key Infrastructure (PKI) simplifying the complete lifecycle management of client certificates.

Unique PSK (UPSK): For BYOD/IoT lacking 802.1X, AGNI offers Unique Pre-Shared Keys (UPSK) as a significantly more secure alternative to MAB or shared PSKs. Each user/device gets a unique passphrase, managed via self-service portals. UPSK can also enable micro-segmentation at the wireless layer.

Secure Communication (RadSec): AGNI secures RADIUS communication using RadSec (RADIUS over TLS), encrypting the entire exchange.

The choice depends on device capabilities and security needs. 802.1X (ideally certificate-based) is preferred for security. Vendor-specific enhancements like AGNI's UPSK or ClearPass Onboard simplify secure access for diverse devices. MAB remains a fallback but requires careful control.

Table: NAC Authentication Method Comparison (Including Vendor Enhancements)

Securing IoT and BYOD Environments with NAC

The proliferation of Internet of Things (IoT) devices and the acceptance of Bring Your Own Device (BYOD) policies introduce significant security challenges. These devices often lack robust security features, may not support standard authentication like 802.1X, run diverse OSes with varying patch levels, and can represent "shadow IT". NAC provides essential tools, with solutions like Cisco ISE, Aruba ClearPass, and Arista AGNI offering specific capabilities to manage these risks:

Device Profiling & Visibility: A critical first step is identifying what is connecting. Modern NAC solutions employ techniques like DHCP fingerprinting, MAC OUI analysis, protocol analysis (HTTP, NMAP, SNMP etc.), and traffic pattern observation to profile devices, even non-802.1X ones. ISE offers extensive built-in and feed-based profiling capabilities. ClearPass provides profiling and integrates with ClearPass Device Insight for enhanced ML-based discovery. AGNI performs profiling and integrates with platforms like Medigate for IoT/IoMT context. This profiling classifies devices (e.g., "HP Printer," "iPhone," "Security Camera," "Unknown IoT Sensor").

Context-Aware Policy Enforcement: Once profiled, NAC enforces specific access policies based on device type, function, trustworthiness, user identity, and posture. Least privilege is applied based on role. An IoT sensor might only reach its management server, while a BYOD device gets internet but not internal servers. Policies can assign VLANs, dACLs (ISE), SGTs (ISE), or MSS-Groups (AGNI).

Posture Assessment: For BYOD (and potentially corporate devices), NAC performs health checks before/during access. This verifies OS patches, AV status, encryption, etc.. ISE integrates with MDM/EMM and uses agents (like Cisco NAC Client). ClearPass uses its OnGuard agent and integrates with UEM/EMM solutions. AGNI integrates with EDR/XDR (CrowdStrike, Cortex) and MDM/UEM (JAMF, Intune, Workspace ONE) via APIs/Concourse Apps. Non-compliant devices can be quarantined or blocked.

Simplified & Secure Onboarding: NACs provide tailored methods for BYOD/IoT. ISE offers self-service portals and certificate provisioning. ClearPass Onboard automates BYOD provisioning and certificate management. AGNI uses its integrated PKI for certificates and UPSK for secure, simple connection for devices without 802.1X, avoiding insecure MAB/shared keys. Self-service portals (often via SSO) empower users.

Guest Access Management: All major NACs provide customizable captive portals for guest registration, authentication (including sponsor approval), and temporary access, typically internet-only.

Dynamic Segmentation Integration: Based on profiling, authentication, and posture, NAC dynamically assigns devices to appropriate network segments (VLANs, dACLs, SGTs via ISE, VLANs/roles via ClearPass, or Arista MSS-Groups via AGNI). This automatically isolates IoT, BYOD, guests, and corporate assets, limiting threat propagation.

Given that many IoT/BYOD devices lack robust security and authentication, relying solely on insecure methods like MAB is insufficient. The combination of sophisticated device profiling (understanding the device and its expected behavior) and NAC policy enforcement becomes paramount. This allows IT to gain visibility and apply context-aware controls (segmentation, restrictions) even for unmanaged devices, mitigating risks associated with shadow IT and the diverse IoT/BYOD landscape.

NAC Integration with Security Ecosystem

Network Access Control does not operate in a vacuum. Its effectiveness is significantly amplified when integrated with other security infrastructure components. This enables greater context sharing, automated responses, and a more holistic security posture. Leading NAC solutions like Cisco ISE, Aruba ClearPass, and Arista AGNI offer extensive integration capabilities.

Key Integration Frameworks:

Cisco pxGrid (Platform Exchange Grid): ISE utilizes pxGrid as its primary framework for bi-directional context sharing with a wide ecosystem of Cisco and third-party security solutions. Partners can publish context (e.g., threat intelligence, endpoint posture) to pxGrid, and subscribe to ISE context (user identity, device type, location, SGTs). pxGrid also enables partners to trigger network actions via ISE (e.g., quarantine).

Aruba ClearPass Exchange: ClearPass uses this framework, leveraging APIs (REST), Syslog, and extensions, to integrate with a broad range of third-party systems including EMM/MDM, SIEM, firewalls, helpdesk tools, and IoT security platforms. It allows for sharing contextual data bidirectionally to enhance policy decisions and automate workflows.

Arista AGNI Concourse Apps / APIs: AGNI employs an API-first approach and leverages CloudVision's Concourse application framework for seamless integration with Arista's portfolio (MSS, NDR) and third-party tools (IDPs, EDR/XDR, MDM/UEM, SIEM, Firewalls, IoT platforms).

Common Integration Points:

Identity Providers (IDPs): All major NACs integrate with AD, LDAP, and leading cloud IDPs (Azure AD, Okta, Google Workspace, Ping) for user authentication and group retrieval.

Firewalls: NAC solutions share user/device identity-to-IP mapping and posture context with NGFWs (e.g., Palo Alto Networks, Fortinet, Check Point). This enables identity-aware firewall policies. Conversely, NAC can receive threat info or instruct firewalls. Arista AGNI uses Cloud Gateway (ACG), while ISE often uses pxGrid for this. ClearPass integrates via APIs/Syslog.

SIEM (Security Information and Event Management): NACs forward detailed logs (auth events, posture, policy violations) to SIEMs (Splunk, Sumo Logic, etc.) for correlation, threat detection, investigation, and compliance reporting.

MDM/UEM (Mobile Device Management / Unified Endpoint Management): Integration with platforms like Intune, Workspace ONE, Jamf allows NACs to leverage device enrollment status and compliance data for posture checks and policy decisions.

EDR/XDR (Endpoint/Extended Detection and Response): Integration with EDR/XDR (e.g., CrowdStrike, Cortex) enables NACs to use endpoint threat/health status in access decisions and allows automated quarantine actions triggered by EDR/XDR detections.

Vulnerability Management (VM): NACs can integrate with VM scanners (Qualys, Tenable, Rapid). Scan results can inform posture assessment, potentially denying access to vulnerable devices.

IoT/Asset Management/CMDB: Integration with specialized platforms (e.g., Medigate) and CMDBs (ServiceNow) provides enhanced device profiling for better classification and policy.

Automated Response (SOAR)

Integration with Security Orchestration, Automation, and Response (SOAR) platforms enables automated responses based on correlated alerts from SIEM/EDR/NDR. A common playbook automatically triggers the NAC (ISE, ClearPass, AGNI) to quarantine or block a compromised/non-compliant device, reducing response times and limiting damage.

When NAC is integrated effectively, it becomes a dynamic component of a defense-in-depth strategy. Bidirectional context sharing and participation in automated response workflows transform NAC into a powerful tool for real-time threat containment and adaptive policy enforcement. While ISE offers deep integration within the Cisco ecosystem via pxGrid/TrustSec, ClearPass excels in multi-vendor environments through ClearPass Exchange, and AGNI provides streamlined integration within the Arista stack and via APIs/Concourse.

Conclusion: Building a Zero Trust Campus with Integrated Solutions

Securing the modern campus network requires moving beyond perimeter defenses and implementing robust internal controls. LAN segmentation, utilizing techniques from foundational VLANs to granular micro-segmentation enabled by solutions like Arista MSS or Cisco TrustSec, is essential for limiting the attack surface and containing breaches. Network Access Control (NAC), delivered by platforms such as Cisco ISE, Aruba ClearPass, or Arista AGNI, provides the critical mechanism for enforcing access policies based on verified identity, device health, and context, addressing challenges from diverse users and BYOD/IoT proliferation.

Neither segmentation nor NAC are "set and forget" solutions. They demand careful planning, ongoing management, continuous monitoring, and thoughtful integration with the wider security ecosystem (SIEM, SOAR, Firewalls). The strength of modern approaches lies in the seamless integration of components—scalable fabrics like Campus VxLAN/EVPN, granular segmentation like MSS or TrustSec, and intelligent access control from AGNI, ISE, or ClearPass—often orchestrated by unified management planes like Arista CloudVision or integrated within broader frameworks like Cisco DNA Center.
By strategically deploying and managing these integrated technologies, organizations can build a more resilient, compliant, and secure campus network capable of supporting business objectives while mitigating the evolving threat landscape, paving the way towards a comprehensive Zero Trust architecture.