How Organizations Can Effectively Assess the Current State of Their Legacy Network (As Part of Their Network Security Transformation)

With increasingly sophisticated cyber threats and complex IT environments, organizations are increasingly recognizing the limitations of legacy network architectures. Traditional network security frameworks often rely on a perimeter-based approach, assuming that everything within the network is trustworthy.

However, as enterprises embrace digital transformation, adopt cloud services, and support a remote workforce, this approach is proving inadequate. The shift toward Zero Trust and Secure Access Service Edge (SASE) models reflects a new understanding of how best to safeguard digital assets in a landscape where “trust” must be continuously verified, not assumed.

Why Assessing a Legacy Network is Critical
A crucial first step in the transition to Zero Trust and SASE is to assess the current state of the legacy network. This assessment is necessary to identify existing infrastructure components, understand current security measures, and reveal gaps and weaknesses that could be exploited in today’s evolving threat landscape. Without a thorough understanding of the legacy network, organizations risk overlooking vulnerabilities, misconfigurations, or outdated systems that may obstruct the transition to Zero Trust and SASE. Moreover, a clear assessment enables decision-makers to strategically plan upgrades, avoid redundant expenditures, and lay out a clear path for modernization.

Key Benefits of a Legacy Network Assessment
Assessing the legacy network provides several key benefits that directly support an organization’s transition to a Zero Trust or SASE model:

Identifying Security Gaps: Many legacy networks have security controls that may no longer be sufficient against modern attack techniques. The assessment reveals areas where security upgrades are necessary to meet the Zero Trust principle of “never trust, always verify.”
Ensuring Compatibility with Modern Frameworks: Legacy hardware and software may not support Zero Trust or SASE’s requirements, such as micro-segmentation, real-time monitoring, or advanced identity and access management. Knowing which elements of the legacy network are incompatible helps plan targeted updates.
Laying the Groundwork for Transformation: Zero Trust and SASE are iterative, long-term transformations. A thorough assessment provides a comprehensive understanding of the current environment, setting a clear starting point for each phase of the journey.

In sum, the initial assessment phase offers a structured foundation, allowing organizations to move forward with confidence, knowing the requirements of Zero Trust and SASE will be met with minimal disruption. A careful and methodical approach in this early stage ensures security enhancements are strategic and cost-effective, reducing risks and future technical debt.

1. Inventorying Existing Infrastructure

Creating an inventory of existing infrastructure is a fundamental step in understanding the scope and scale of the legacy network. This inventory will include networking devices, applications, data repositories, endpoints, and user data, all of which play critical roles in the organization’s security posture and network functionality. Here’s a breakdown of each component and its importance:

Identifying Networking Devices and Assets
Legacy networks are typically composed of various hardware devices that work together to facilitate data transfer, communication, and connectivity across different segments of the network. These devices are essential to understand and document during the assessment, as they will serve as the backbone of network operations in a transformed environment. Key networking devices include:

Routers: Routers direct traffic between different segments of the network and connect internal network segments with external networks. Assessing the functionality, security features, and configuration of routers is crucial, as they are often the first line of defense against external attacks.
Switches: Switches facilitate communication between devices on the same network segment. Outdated switches may lack modern security features, such as support for Virtual Local Area Networks (VLANs) or network segmentation capabilities, which are essential for Zero Trust and SASE.
Firewalls: Traditional firewalls protect the network perimeter, but they may need to be updated or reconfigured to support Zero Trust principles, such as micro-segmentation and continuous monitoring. Firewalls that only inspect traffic at a single point could miss malicious activities within the network.
VPN Appliances: Virtual Private Networks (VPNs) have traditionally been used to secure remote connections, but legacy VPN appliances may not support the access control and inspection capabilities required for Zero Trust or SASE.
Other Security Appliances: Intrusion detection systems (IDS), intrusion prevention systems (IPS), and data loss prevention (DLP) systems are also vital to assess, as many legacy models may lack the compatibility or adaptability needed for Zero Trust’s rigorous security posture.

Creating a comprehensive list of these devices, along with their location, age, firmware/software version, and functionality, provides a strong foundation to identify which equipment needs upgrading, reconfiguration, or replacement.

Applications and Data Repositories
Beyond physical infrastructure, organizations must also inventory applications, databases, and other repositories where data is stored and processed. Understanding the full scope of applications and data assets is essential for a few reasons:

Application Mapping: Documenting applications helps clarify which systems and services rely on legacy technology and where interdependencies exist. Many applications may not support modern authentication standards or encryption protocols, making them potential weak points in a Zero Trust or SASE framework.
Database Locations: Legacy networks may include on-premises databases, cloud storage, and other data repositories, each with unique access and security requirements. Identifying where critical or sensitive data resides enables organizations to focus security resources on protecting these assets.
Data Sensitivity Levels: Not all data is created equal. By cataloging data repositories and classifying data based on sensitivity and regulatory requirements, organizations can prioritize protection measures. Zero Trust and SASE both emphasize the importance of context-based access control, and understanding data sensitivity levels is critical to implementing effective policies.

Inventorying applications and data repositories also highlights potential data migration challenges, such as compatibility with cloud platforms, data integrity concerns, and compliance with data privacy regulations, all of which must be addressed during the transformation process.

Endpoints and Users
Modern organizations rely on a vast array of endpoints and users with access to network resources. Legacy network environments often lack the granular control required to manage and monitor all endpoints effectively. A thorough inventory of these components includes:

Connected Devices: Document all devices connected to the network, including laptops, desktops, mobile phones, and IoT devices. Each of these endpoints represents a potential entry point for attackers and must be accounted for in a Zero Trust or SASE strategy.
Remote and Mobile Workforce: Many organizations now support remote work, creating challenges for legacy networks that were not designed with mobility in mind. Zero Trust and SASE frameworks are built to secure distributed workforces, but legacy networks often lack the tools to verify and monitor remote connections effectively.
User Accounts and Permissions: A comprehensive user inventory that includes roles, access permissions, and activity levels is essential for establishing a Zero Trust architecture. Overly permissive or poorly monitored user accounts are common in legacy networks, increasing the risk of insider threats or compromised credentials.

By cataloging all endpoints and users, organizations can identify areas where access control needs to be tightened or where additional monitoring is necessary. This information is foundational for implementing the principle of least privilege and continuous verification required in Zero Trust.

Importance of Comprehensive Inventorying
A detailed inventory of network devices, applications, data repositories, endpoints, and users does more than simply list assets. It reveals crucial insights that shape the security transformation process and drive informed decision-making. Here’s how:

Uncovering Hardware Limitations: Many legacy hardware devices have limited capabilities compared to modern equipment. For instance, an older router may not support the encryption standards or segmentation features necessary for Zero Trust. Knowing these limitations early allows organizations to prioritize hardware upgrades where they are most needed.
Identifying Network Fragmentation: Legacy networks can become fragmented over time as organizations add new devices, applications, and network segments to accommodate growth. Fragmentation leads to increased complexity, which is challenging to secure and monitor. A comprehensive inventory helps map these fragmented areas, enabling a smoother transition to a more cohesive and secure architecture.
Detecting Outdated Software and Firmware: Legacy systems often run on outdated software that lacks support for modern security protocols. For instance, applications that do not support multi-factor authentication (MFA) or devices that lack firmware updates are significant vulnerabilities. Identifying these gaps early allows for targeted software updates or replacements.
Preparing for Compatibility Challenges: Some legacy devices and applications may not be compatible with Zero Trust or SASE models. For example, an application that requires unrestricted network access may not align with Zero Trust’s principle of restricted, conditional access. Early identification of these issues ensures that IT teams can plan for compatibility adjustments or replacements as necessary.

In summary, inventorying the existing infrastructure is not merely a documentation exercise—it’s a critical step that forms the foundation of a robust security transformation strategy. By understanding every asset within the legacy network, organizations are empowered to take targeted, effective actions that streamline their journey to Zero Trust and SASE, reducing risk, enhancing security, and supporting long-term adaptability.

2. Mapping Network Traffic and Data Flows

Mapping network traffic and data flows is essential to understanding how information moves within and beyond an organization’s boundaries. This process reveals potential vulnerabilities, uncovers inefficient traffic patterns, and supports compliance efforts by illuminating where sensitive data resides and how it’s accessed.

Traffic Flow Analysis

Mapping Data Paths: Begin by identifying each segment of your network, including on-premises systems, remote locations, and cloud environments. Use network mapping tools to visualize traffic routes and connections, focusing on both internal data movements (like inter-departmental traffic) and external paths (such as connections to third-party services and cloud providers).
Understanding Data Interactions: Document which systems and applications interact and what type of data is exchanged. For example, a company database might connect to a CRM, HR, or analytics platform. Understanding these connections helps anticipate where Zero Trust or SASE controls, like micro-segmentation, should be placed.
Real-Time Monitoring and Historical Logs: To map accurately, use real-time monitoring tools to observe current traffic and historical log data to understand typical flows. Network behavior analytics tools can also help identify unusual patterns, which may signal potential threats or inefficiencies.
Cross-Environment Flow Analysis: For organizations with multi-cloud or hybrid setups, mapping data flows between cloud environments (like AWS to Azure connections) is critical. These flows often involve different compliance considerations, configurations, and potential vulnerabilities.
End-to-End Ownership and Responsibility: Assign owners for each data flow path, from application to endpoint, to ensure accountability for data management and security. This helps in incident response, as the responsible team will be better equipped to act quickly in case of a breach.

Identifying Chokepoints and Bottlenecks

Locating Latency Issues: Traffic bottlenecks can cause latency, impacting user experience and system efficiency. Identify where data processing is slowed due to outdated infrastructure, limited bandwidth, or improperly configured network devices.
Detecting Single Points of Failure: Many legacy networks have single points of failure—vulnerable points where, if a device or path fails, entire network sections can become inaccessible. Redundancy planning in critical areas can mitigate this.
Security Gaps in Traffic Paths: Look for network segments where security controls are weak or absent. Common chokepoints, such as legacy routers or firewalls without robust inspection capabilities, can leave data flows exposed to threats.
Traffic Prioritization: Classify network traffic based on importance and urgency, using protocols like Quality of Service (QoS) for prioritized handling of critical applications. This reduces bottlenecks, especially in networks supporting remote or cloud workloads.

Data Sensitivity and Compliance Considerations

Data Classification: Identify and classify data as sensitive, public, regulated, or internal. Sensitive and regulated data flows—such as financial, personal, or health information—require enhanced protection and compliance with regulations like GDPR or HIPAA.
Regulatory Data Handling: Regulatory requirements often dictate specific handling of certain data types. Ensure that sensitive data does not cross unsecured or non-compliant network paths. For example, certain data flows may need encryption or segregation based on compliance mandates.
Policy-Based Routing: Implement policy-based routing that directs sensitive data flows through dedicated, monitored, and secure paths. For example, data involving financial transactions may be directed through specialized, encrypted paths.
Continuous Data Monitoring: Real-time monitoring is essential to detect unusual patterns or unauthorized access attempts to sensitive data flows, enabling proactive response to potential compliance breaches or security threats.

3. Evaluating Current Security Policies and User Access

To create a Zero Trust or SASE-compatible network, organizations must scrutinize and update existing security policies and user access protocols. This evaluation will ensure security policies are not only relevant but also enforceable across all devices and locations.

Security Policy Review

Evaluating Policy Scope: Assess whether current security policies cover all aspects of network access, including local, remote, mobile, and cloud-based systems. Gaps in coverage—such as unregulated remote access—could lead to exploitable vulnerabilities.
Assessing Access Control Mechanisms: Review access control mechanisms, including login requirements, multi-factor authentication (MFA), and user verification procedures. Ensure that access to sensitive resources requires MFA, as single-factor authentication can be a major weak point.
Frequency and Consistency of Policy Updates: Policies need to evolve with new threats and organizational changes. Review how often they’re updated and whether policy changes are promptly applied across all network locations and devices.
Standardization Across Environments: Ensure that security policies are consistent across cloud and on-premises environments. Variations in policy enforcement between environments may expose certain areas to threats that aren’t mitigated elsewhere in the network.

User Access Rights and Permissions

Applying the Principle of Least Privilege (PoLP): Review user access levels, granting the minimum access needed for each role. Unchecked or overly broad permissions can lead to unauthorized data access or exploitation by malicious insiders.
Admin Account Restrictions: Special attention should be given to administrative accounts, which often have extensive privileges. Limit these accounts to essential users only, monitor their activity, and enforce MFA.
Auditing Privileged Access Logs: Keep detailed logs of access attempts and activities associated with high-level or sensitive accounts. This can reveal patterns or anomalies indicating misuse or account compromise.
Access Verification Mechanisms: Ensure users are periodically prompted to re-authenticate, particularly when accessing sensitive data or resources from new or remote devices.

Policy Enforcement Consistency

Uniform Policy Application: Evaluate the use of automated configuration tools that apply policies uniformly across all environments. This reduces discrepancies and enhances the reliability of security protocols.
Configuration Management: Utilize configuration management tools to detect and correct policy drifts. Network infrastructure changes can lead to configuration gaps where enforcement may weaken.
Audits and Penetration Tests: Conduct periodic audits and penetration testing to verify that security policies are being effectively enforced. These activities expose weaknesses that standard reviews may miss, ensuring your policies are as robust as possible.

4. Identifying Security Gaps and Vulnerabilities

Identifying and addressing vulnerabilities in a legacy network is essential for aligning with Zero Trust and SASE frameworks. This process includes a thorough gap analysis, vulnerability assessment, and prioritization of risks.

Gap Analysis

Benchmarking Against Zero Trust and SASE Standards: Compare your network against best practices to identify areas for improvement. For example, Zero Trust requires identity-based access, which may be missing in legacy setups.
Key Control Review: Look for gaps in core security controls, such as multi-factor authentication, encryption, and micro-segmentation. Missing or outdated controls can be points of failure in a Zero Trust model.
Legacy Constraints: Some legacy components may be inherently incompatible with Zero Trust principles, lacking in areas like identity-based access control or real-time data monitoring.

Vulnerability Assessment

Unpatched Systems and Devices: Regularly audit network devices for outdated software or unpatched firmware, which can be exploited by attackers.
Application Security Gaps: Assess web and internal applications for vulnerabilities, especially those that handle sensitive information or operate in internet-facing environments.
Weak Access Control Points: Identify unmonitored or minimally protected access points, such as old VPNs or unsecured guest networks, and prioritize them for upgrade or segmentation.

Risk Prioritization

Assessing Risk Severity: Rate each vulnerability based on its potential impact, likelihood, and exposure risk. Address high-severity risks immediately, like unpatched critical systems.
Immediate vs. Long-Term Fixes: Differentiate between quick fixes, such as implementing MFA, and longer-term upgrades, such as transitioning to newer devices that support SASE features.
Resource Allocation: Use your prioritization to guide budget and resource planning, focusing on the most impactful fixes to maximize security improvements.

5. Documenting Findings and Creating an Action Plan

Documenting findings and creating a clear, structured action plan are key steps in transitioning from a legacy network to a modern, secure environment using frameworks like Zero Trust and SASE. Proper documentation serves as a roadmap for the entire transformation process, ensuring that all issues are addressed, resources are allocated effectively, and progress is measurable.

Comprehensive Documentation

The first step in any network security transformation is documenting the findings from the assessment. Without comprehensive records, it’s nearly impossible to track progress, identify gaps, or allocate resources effectively. The documentation process should be thorough, capturing all aspects of the legacy network’s current state. Key areas to include in this documentation are:

Inventory Summary
- Hardware and Infrastructure: Begin by listing all the networking devices in the organization’s environment. This includes routers, switches, firewalls, load balancers, and any other physical or virtual appliances. Record their make, model, firmware version, and any known limitations. This helps identify legacy equipment that may need to be upgraded or replaced in the transition to a Zero Trust/SASE framework.
- Applications and Services: Document all the critical applications, databases, and cloud services in use, as well as how they interact with each other. Include data flows, the types of data processed, and where the data is stored or transferred (e.g., local servers, cloud storage).
- Endpoints and Devices: Keep a record of all endpoints, including IoT devices, remote workers’ laptops, mobile devices, and workstations. Understanding the total number of endpoints in use and their access patterns will help pinpoint areas of vulnerability and where to implement more granular security controls like micro-segmentation.
Network Traffic Maps
- A key part of documentation is visualizing how traffic flows across the network, both internally and externally. This should include:
  - Internal Traffic: Map how data moves between on-premises systems, between departments, and across internal networks. Note any sensitive data flows, high-volume traffic, or legacy systems that could slow down performance.
  - External Traffic: Include data flows from internal systems to external systems, including connections to the cloud, third-party services, VPNs, and remote devices. It’s essential to identify weak points where traffic might be exposed or unencrypted.
  - Data Sensitivity and Compliance: Mark any areas where sensitive data is transmitted, especially if it crosses multiple jurisdictions. This mapping helps ensure compliance with regulations like GDPR, HIPAA, or CCPA, which may require specific protections for sensitive data flows.
Identified Vulnerabilities and Security Gaps
- Summarize the findings from the vulnerability assessment. This includes identifying:
  - Outdated Systems: Systems that are running outdated software or firmware that no longer receive updates from vendors, making them susceptible to known vulnerabilities.
  - Weak Access Controls: Highlight any instances of poorly enforced access control, such as shared accounts, lack of multi-factor authentication (MFA), or improper user permission settings.
  - Chokepoints or Single Points of Failure: Identify any areas where network bottlenecks or critical systems are vulnerable to disruption or attack. These may include old routers, firewalls, or misconfigured systems.
  - Compliance Gaps: Document areas where the organization is not in full compliance with relevant regulatory standards or internal security policies, which will need to be addressed during the transition to Zero Trust/SASE.

This documentation serves as a living record that can be referred to during the entire transformation process. It allows the team to measure progress, validate improvements, and ensure that no critical aspect is overlooked.

Setting Priorities

Once the assessment is documented, the next step is to prioritize actions based on risk level, impact, and cost. Prioritizing actions ensures that the organization focuses on the most critical security gaps and addresses them efficiently. There are several methods to prioritize actions, but it’s important to follow a risk-driven approach.

Risk-Based Prioritization
- Severity of Vulnerabilities: Assess the severity of each vulnerability or gap. Critical vulnerabilities that can easily be exploited, such as unpatched firewalls or outdated software that supports legacy protocols, should be addressed first. These can be entry points for cyber-attacks and thus represent the highest risk to the organization.
- Potential Business Impact: Consider the potential business impact of each vulnerability. For example, a security gap in a cloud application that holds customer data might have a greater impact than a gap in a non-sensitive internal tool. The potential for reputational damage, regulatory fines, or business interruption should guide the prioritization.
- Likelihood of Exploitation: Consider how likely it is that each vulnerability will be exploited. A weakness in a high-profile public-facing system is likely to be targeted more quickly than a gap in an isolated internal network. Similarly, a misconfigured VPN for remote workers poses a higher risk of compromise compared to a legacy router that is isolated from the rest of the network.
Cost of Remediation
- Immediate vs. Long-Term Fixes: Prioritize fixes based on their urgency and complexity. Some issues can be resolved quickly and cheaply—such as applying patches or updating access permissions—while others, such as replacing legacy equipment or reconfiguring network architecture, may take more time and resources.
- Resource Allocation: Ensure that the most critical issues are addressed first, allocating resources accordingly. While some issues may be urgent, others may be handled in a phased approach, especially if they involve significant capital expenditure.
- Cost-Benefit Analysis: For each remediation task, perform a cost-benefit analysis. Evaluate the cost of implementing the fix (including labor, hardware, and software) versus the expected benefit (reduced risk, improved performance, compliance, etc.). This can help ensure that resources are allocated in the most efficient way.

By considering severity, impact, and cost, organizations can develop a clear set of priorities that will guide the remediation process.

Defining Next Steps

Once priorities are set, the next critical step is to create a structured, actionable roadmap that defines the sequence of activities to modernize infrastructure and implement Zero Trust and SASE principles. This roadmap should break down the process into manageable phases, ensuring that each phase aligns with business objectives and security goals.

Developing a Roadmap
- Phased Approach: Start by addressing the highest-priority vulnerabilities and gaps. For instance, if outdated firewalls are identified as a high risk, replacing or upgrading them should be a first priority. Similarly, implementing basic Zero Trust principles, such as identity-based access and MFA, should be a priority early in the process.
- Short-Term and Long-Term Goals: Create a clear distinction between short-term and long-term actions. Short-term goals might involve quickly patching systems or enforcing access control policies, while long-term goals could involve re-architecting the network, implementing SASE for secure access, or migrating to a cloud-native infrastructure.
- Milestones and Timelines: For each phase of the roadmap, set clear milestones and timelines. Break larger tasks into smaller, more manageable steps to track progress more effectively. Regular check-ins or project reviews should be scheduled to ensure the team stays on track and can adjust to new requirements or challenges.
Implementing Zero Trust and SASE Gradually
- Initial Zero Trust Implementation: Begin with the easiest Zero Trust principles to implement, such as identity verification (strong authentication) and access control enforcement. These can be applied to existing systems with minimal disruption.
- Micro-Segmentation: Gradually implement network segmentation to limit lateral movement within the network. Start with the most critical areas, like sensitive data repositories, and expand to other parts of the network as the infrastructure evolves.
- SASE Integration: For organizations adopting SASE, the transition involves the gradual replacement of traditional perimeter-based security models with cloud-native security functions. This could involve integrating Secure Web Gateways (SWG), CASB (Cloud Access Security Broker), and SD-WAN technologies into the network.
Continuous Monitoring and Adjustments
- Progress Metrics: Establish key performance indicators (KPIs) to track the progress of the security transformation. These might include metrics like the number of vulnerabilities closed, the completion of critical upgrades, or the deployment of Zero Trust technologies.
- Iterative Improvements: Security transformation is an ongoing process. As new vulnerabilities are identified or business needs change, the roadmap should be adjusted. Regularly revisit the documentation and action plan to ensure the organization’s security posture evolves as threats and technologies evolve.

By systematically documenting findings, setting clear priorities, and defining a structured roadmap, organizations can smoothly transition from legacy networks to secure, modern architectures based on Zero Trust and SASE principles. This approach minimizes risk, optimizes resource allocation, and ensures the security transformation is comprehensive and aligned with both business objectives and regulatory requirements.

Conclusion

The most disruptive phase of network transformation isn’t the implementation of new technologies but the careful evaluation of what already exists. A thorough assessment of a legacy network provides the clarity needed to make informed decisions, laying the groundwork for a seamless shift to Zero Trust and SASE.

Rather than simply identifying gaps, this process uncovers opportunities for improvement, enabling organizations to proactively address vulnerabilities before they escalate into security breaches. This foundational step ensures that every phase of the transformation is strategically aligned, from updating infrastructure to enforcing modern security policies.

With a clear understanding of the existing environment, organizations can avoid costly missteps and ensure that their security framework evolves in tandem with emerging threats. The insights gained from mapping traffic flows, reviewing policies, and identifying weaknesses are indispensable in shaping a future-proof network.

The next step is to prioritize high-risk vulnerabilities and ensure that immediate action is taken to mitigate those risks. From there, developing a phased, actionable roadmap is essential for successfully integrating Zero Trust and SASE into the organization’s daily operations. This phased approach will facilitate a gradual but steady transition, ensuring that security measures are not only effective but scalable. Over time, the legacy gaps will close, and the security posture will strengthen, empowering the organization to better respond to both internal and external threats.

As organizations embrace these new frameworks, they will find that continuous monitoring and ongoing adjustments are key to maintaining a resilient and adaptive security environment. Finally, the results of a well-executed network assessment ripple across the entire IT infrastructure, fostering a culture of proactive security that positions the organization for sustained success.