Network Segmentation - Stopping Lateral Movement

About 2 min read

Network segmentation is a technique that divides an organization's network logically or physically into multiple segments (zones) and restricts communication between segments using firewalls and access control lists. Even if an attacker breaches one segment, the damage can be localized by preventing lateral movement to other segments. As of 2025, with the spread of zero trust architecture, the adoption of microsegmentation is accelerating.

Real-World Use Cases

"Ransomware infected a terminal in the accounting department, but thanks to VLAN-based segmentation, we were able to prevent lateral movement to the development environment and production servers. Because the infection was confined to a single segment, recovery was completed in just four hours."

Conceptual Diagram of Network Division

Segmentation Methods

Physical segmentation separates networks using dedicated switches and routers; it is the most reliable but the most costly. Logical segmentation using VLANs (virtual LANs) can separate multiple networks on a single switch and offers excellent flexibility. Microsegmentation is the latest approach, based on the concept of zero trust, that controls communication at the workload level.introductory books on network design (Amazon) offer a systematic way to learn.

Design Points in Practice

PCI DSS defines as a requirement that systems handling cardholder data be separated from other networks. A common design is based on four zones: a server segment, a user segment, a DMZ, and a management segment, subdivided further according to business requirements. As a principle, communication rules between segments should follow "default deny," and a whitelist approach that explicitly permits only the necessary communication is recommended. Protect the management consoles of network devices with strong random passwords to prevent unauthorized changes to segmentation rules.books on zero trust networks (Amazon) are also a useful reference.