The concept of network segmentation has been around for (seemingly) ever. So much so that many folks can forget just how essential it remains for locking down your network against the growing cybersecurity threat landscape. I like to think of network segmentation security as akin to a home that includes super strong, reinforced, keyed interior doors between every room. Even if an intruder gains access to a particular room from an exterior access point like a door or window, they get no further than that and cannot move elsewhere in the house. Just so with an effectively segmented network where a hacker gains malicious access to say, the guest network is left with no ability to move “laterally” and expand their movement to sensitive IT resources. In this blog, I’ll provide crucial network segmentation information you must know to protect your environment and on which you can build strong cybersecurity fortress.
What is Network Segmentation?
Network segmentation is all about dividing so your (network) cannot be “completely conquered”, meaning a hacker gains access to one portion of the network and then moves laterally to other areas of the environment resulting in significant swathes or all of it being compromised. The cool way of expressing this is “splitting [the network] reduces the “blast radius” or damage a hacker can accomplish should they gain entry.
Network segmentation security, dividing the network and restricting access between logical or physical segments can be accomplished using one or combination of the following methods:
- VLANs
- Subnets
- Firewall zones
- Software-defined groups
Network segmentation can be further implemented broadly (macro-segmentation) by, for example partitioning between human resources and finance or all OT/IoT devices. Alternatively, it can be done with detailed specificity (micro-segmentation). An example here would be “the accounting department app hosted on this server can only talk to a specific port of a particular database server”. Whatever the method(s) used, network segmentation security limits damage when a breach occurs, improves monitoring, and helps enforce least privilege.
The Big 5 Tasks to do for Effective Network Segmentation
Here’s the big items, in order of importance that you must do ASAP to effectively implement network segmentation in your environment:
Step 1: Know your network inside and out – What does this mean? Comprehensively map your network, every asset, app and the valid communications between them. Begin with an in-depth inventory and remember it is EASY to miss devices at the edge even with best-in-class security tools. Once this is done, quantify the apps and services by asking: Which protocols and ports are being utilized? Effective network segmentation security depends on getting this right, then making sure new devices and services are accounted for when introduced.
Step 2: Form (design) follows function – Don’t begin network segmentation by thinking of IP addresses. Instead, scrutinize your network environment by business purpose, keeping a sharp eye on risks to the organization. Group by importance and sensitivity, accounting versus guests, but also by function—printing and VoIP, and finally by device types (e.g., client, IoT, hosts). Now, build out useful zones based on your analysis of these many variables. The key is to view this from an organizational perspective on how the business actual works. Now is the time to build out IP address lists! Remember: Fewer, well-thought-out segments beat dozens of VLANs generated willy-nilly every time!
Step 3: Think big, then small – It’s best to begin with large (macro segmentation), but logical segments. This might include a separate guest Wi-Fi network, user LANs, and perhaps headless devices like IoT and OT. Then, get specific with micro-segmentation, considering crucial network resources such as databases, domain controllers, and control-planes. Here too can be added highly sensitive functions or services like payroll or development. Deploying from “top-down” helps reduce possible disruption and allows for rigorous segment testing before going live.
Step 4: Stringent policy enforcement – This can be achieved by utilizing firewalls, ACLs, next-gen rules, identity-aware proxies, or software-defined groups. These network segmentation security methods can apply policies based on user identity, device posture, and app intent without only using IP addresses. Policies should always be tied to business needs: Who and what needs access, not to arbitrary network IP addresses.
Step 5: Continuous, ongoing monitoring and testing – Network segmentation security is never won and done. Instead, to the extent possible constant assessment to validate the implemented network segmentations remain robust are essential. Consider open-ended review of flow and other logs and periodic pen testing. Because of its dynamic nature, the network perimeter merits heightened scrutiny as it is here that hackers often get their foothold.
What can happen when your network is not properly segmented?
“With so many cyber attacks in the headlines, our message is clear: every organisation, no matter how large, must take proactive steps to keep people’s data secure,” said John Edwards, UK Information Commissioner.
ICO said Capita failed to implement adequate measures to prevent privilege escalation and unauthorised lateral movement through its network, and did not respond effectively to security alerts.”1
Network Segmentation Actions to Avoid
- Whack a mole VLANs – “When in doubt, create another VLAN” is not a good idea. Simply adding another VLAN based on a hunch or to assuage lingering concerns about your current network segmentation security efforts without filtering and routing controls can cause a false sense of security. The bad guys can circumvent and succeed in moving laterally if layer-3 rules are lax.
- Too much segmentation can be a problem – Be sure you have a good reason to add another network segment. Excessive zones, especially small ones, can generate management chaos and increased error rates caused by mis-directed or erroneously blocked traffic. Refer to Step 2 above.
- Deemphasizing the network edge – Guest networks, cameras, and printers are frequently a “field of sweet dreams” for hackers to gain (easy) access to your network. Be certain your guest network is nailed down solid and keep track of things like cameras and printers. Adding devices such as these and other headless assets like IoT—often without IT being involved—in the wrong place or without filtering for east-west traffic can be highly risky and serve as a massive attack vector. Step 1 above is critical to mitigation of this threat.
Biggest Network Segmentation Errors
| # | Error | Result |
| 1 | Poor network inventory / no topology mapping (This includes not maintaining up-to-date lists or maps as well.) | You are flying blind from an IT operational perspective. Any sub-par network segmenting done will leave potentially gaping security holes, could negatively impact legitimate traffic, and/or could break apps or services |
| 2 | Excessively permissive network segmentation | Rules like “allow any VLAN x to y” is best viewed as a wide-open door for hackers who upon gaining access easily move laterally, resulting in a potentially large blast radius should (when) they succeed |
| 3 | Weak (or non-existent) change control and testing | Making updates to network segmentation without carefully aligning with proper change controls and rigorous testing can take down mission critical apps and/or services outages |
| 4 | One-off network segmentation initiatives | Today’s networks are incredible dynamic with devices, network, apps, and services in a constant state of flux; the need for continuous re-assessments of network segmentation security is critical so as to limit increased organizational risk |
Summary
Ongoing and continuous network segmentation security assessments are critical to maintaining peak cybersecurity posture. The great news is, the ROI of your efforts is enormous and has the added bonus of providing you with in-depth intelligence and situational awareness into your entire IT environment. By following the steps provided above, you will gain confidence in your ability to deliver peak optimal services securely and sleep better at night as well! When it comes to successfully deployments, be sure to consider tools like CyberScope® that can offer complete asset observability at the
Additional Resources
- OWASP – Network Segmentation Cheat Sheet
- Check Point – Network Segmentation vs Micro-Segmentation
- Security Boulevard Macro Segmentation vs. Micro Segmentation
- CIS Critical Controls Network Segmentation Based on Sensitivity
1UK’s Capita fined $19 million for 2023 cyber breach | Reuters, October 15, 2025
