Building Resilient Networks: Limiting the Risk and Scope of Cyber Attacks

In the current era of nearly ubiquitous computing, security threats are growing, especially for large organizations that have to maintain complex networks and safeguard sensitive data. While this complexity has also led to the proliferation of a wide range of tools available to organizations to boost network security, a foundational strategy still remains one of the most effective ways to protect organizational networks: that of network segmentation. However, network segmentation as a tool has stayed far from stagnant, with recent developments and innovations turning it into a more complex and sometimes misunderstood topic. In this article, we will explore what network segmentation is, why it's important, and how it can be applied to optimize network performance and security. 

Network Segmentation: The “Why”

Network segmentation refers to the practice of dividing a computer network into several smaller component “segments” which are somewhat isolated from each other due to having individual security restrictions and policies such as access controls and firewalls. These segments can vary in size, function, and design depending on what the organizational requirements are, such as security levels, data and systems sensitivity, and performance requirements. 

Network Segmentation Strategies

 Network Segmentation isn’t a monolith: there are a few different ways that it’s implemented in network architecture in the real world. These include: 

Macro-Segmentation

Macro-segmentation, the oldest and most commonly used segmentation methodologies, divides the network into a number of large, broadly defined segments that are then separated from each other through network security mechanisms like access control lists (ACLs) and firewalls. Communication between these different zones must pass through the firewall each time. Through this approach, one compromised segment can still be contained, without other segments being affected. In the traditional model, segmentation stops here: within the segments, traffic still flows freely.  

Zone Segmentation

A middle layer between macro and micro-segmentation, zone segmentation is very similar to macro-segmentation (to the point where many don’t distinguish between the two at all), being another layer of segmentation by zone within the broader segments. This segments-within-segments approach is often used when different resources, or resource groups, have different levels of sensitivity within the broader segment. However, zone segmentation is still distinct from micro-segmentation as the segmentation is still enforced at the TCP/IP level, unlike with micro-segmentation. 

Micro-Segmentation

Finally, we have the most cutting edge and complex to implement form of segmentation, micro-segmentation. Micro-segmentation takes the same general principle from macro and zone segmentation but applies to it at a much more granular level. Instead of segmenting at the zone level or broader, micro-segmentation brings the perimeter to the resource level, applying security controls to the individual host. This involves the use of software defined networking technologies, or SDN for short, as well as virtualization to apply security policies at a granular level.

Challenges of Network Segmentation

Complexity: For all levels of network segmentation, complexity is a major drawback. With macro and zone segmentation, the scale of different security rules, from firewalls to ACLs, software controls, and VLANS can become a daunting task to manage, requiring careful planning and execution. Similarly, with micro-segmentation, the advantage of granular control has the drawback of massively increasing the number of policies that have to be managed. 

Performance: Network performance can also be hampered by segmentation, as passing traffic through security devices creates bottlenecks, slowing down the network. Additionally, micro-segmentation requires most traffic to be encrypted, which also impacts network performance as the encryption and decryption process requires more time and resources. However, these performance drawbacks can be mitigated with a well-designed segmentation architecture. 

Combined Segmentation: The Ideal Approach

While each of the segmentation techniques has their individual merits, the optimal approach combines the virtues of macro, zone, and micro-segmentation to maximize the security provided. Macro-segmentation provides a broader framework for the network, while within the broad segments, micro-segmentation can be applied to specific resources and workloads, to create a true defense-in-depth setup and move an organization towards a zero-trust framework, of which segmentation is a key component. 

Best Practices for Network Segmentation

Now that we’ve covered the key elements of what constitutes network segmentation, the question remains: how does an organization go about implementing segmentation in a way that effectively increases network security? One key to success is the use of best practices when it comes to network segmentation. These include:

Employ the Principle of Least Privilege

The principle of the least privilege is a simple, but nonetheless powerful one. To use the Wikipedia definition, the principle dictates “giving any user accounts or processes only those privileges which are essentially vital to perform its intended functions.” There are a number of strategies to enforce the principle, some of which are mentioned below, but thinking about whether the least privilege is being met whenever security policies are being considered for implementation is key for maximizing network security.

Use VLANs, Firewalls, Software, and Other Key Security Devices

VLANs are a powerful tool for segmenting a network without the need for additional physical devices. They help isolate traffic between departments, applications, or different security zones. Similarly, properly set up firewalls and software perimeters can increase security by decreasing the attack surface and preventing breaches from spreading. 

Implement Strong Access Control Policies

Who can access each network segment can be managed through the use of firewalls, access control lists (ACLs), and role-based access control (RBAC) to restrict traffic flow. In conjunction with the least privilege principle, access control policies result in a tighter, better managed, and therefore more secure network, with ACPs adding another layer of security to each segment and ensuring sensitive data remains protected.

Monitor Traffic Between Segments

Even though segments are isolated, traffic still needs to pass between them at times. Implementing monitoring and intrusion detection systems that track cross-segment traffic for signs of unusual activity can help to nip security breaches in the bud. 

Regularly Review and Update Segmentation Plans

Networks are constantly evolving, and segmentation strategies must evolve alongside them. Organizations should regularly evaluate and update their network segmentation policies to ensure they align with current security threats, performance requirements, and organizational needs.

Conclusion

Network segmentation is an essential aspect of modern network architecture, offering improved security and limiting the scale of the damage when breaches do happen. By effectively dividing a network into smaller, isolated segments, organizations can minimize risks, reduce the attack surface, and protect themselves from costly and damaging cyberattacks and network disruptions from malicious actors. Whether using macro, zone, or micro-segmentation, or ideally a combination of all three, it is important to plan the design thoughtfully and implement best practices to ensure that the segmentation strategy supports both current and future network requirements and does its job in increasing the organization’s network security. 

As organizations grow and adapt to new technologies and threats, the importance of network segmentation will only increase, making it a critical tool for network security. Thanks for reading!