May 07, 2025
WRITTEN BY: ZACHARY SPRENGER
Network
Segmentation: Enhancing Security and Access Control
In my 20 years of working in the IT
industry, primarily with small business customers, I have rarely encountered
networks large enough to require segmentation. However, with small businesses
far outnumbering large corporations, adopting security measures from enterprise
environments can be essential. This article outlines the importance of network
segmentation and practical use cases for its implementation.
Why Network Segmentation
Matters
Network segmentation enhances security by limiting access between network-connected devices, reducing an attacker's ability to move laterally through a network. Here are key reasons why segmentation is critical:
1. Obfuscation from Attackers:
○
One of the first actions a bad
actor takes upon infiltrating a network is performing a ping sweep to map connected devices.
○ If segmentation limits the number of visible devices, an attacker may perceive the network as too small to target and move on.
2. Isolation of Critical Systems:
○
Legacy systems, management
interfaces, printers, vendor devices, and PCI-compliant
payment systems should not share the same network as standard users.
○ This prevents unauthorized access and minimizes exposure to security vulnerabilities.
3. Guest Network Security:
○
Employees' personal devices and
visiting vendors should connect to a separate
VLAN to prevent potential threats from reaching the main network.
Practical Use Case: Small
Business Implementation
Consider a small business with the
following network infrastructure:
●
20 Desktop Computers
●
4 Laptop Computers
●
2 Wireless Access Points
●
3 Network Printers
●
2 Servers
●
1 Time Clock (connected to a cloud service)
This business allows employees to connect
personal devices to Wi-Fi and provides guest access to vendors. The recommended
segmentation strategy would be:
VLAN Assignments
|
VLAN |
Purpose |
|
VLAN
10 |
Time Clock (restricted to vendor's required
ports for internet access) |
|
VLAN
20 |
Admin Network (desktops and laptops) |
|
VLAN
30 |
Server Network |
|
VLAN
40 |
Printer Network |
|
VLAN
50 |
Guest Wireless Network |
|
VLAN
60 |
Employee Wireless Network |
Access Control List (ACL) Rules
Access between VLANs should be carefully
restricted using ACLs to enforce the
principle of least privilege:
●
Admin VLAN (20)
→ Allowed to communicate with Server VLAN (30) on DHCP, DNS, SMB, NTP, and
specific application ports (as defined by vendors).
●
Printer VLAN (40)
→ Allowed to communicate with Server VLAN (30) on HTTP, HTTPS, and print
service protocols (for print server integration).
●
Time Clock VLAN (10)
→ Allowed outbound internet access only on required vendor ports; no internal
network access.
●
Guest VLAN (50)
→ Completely
isolated from internal business networks.
●
Employee VLAN (60)
→ No direct access to Admin VLAN (20) or Server VLAN (30)—internet access only.
Security Benefits of
Segmentation
Without VLANs, all devices would reside
on the same network, creating multiple risks:
●
A compromised IoT device, like a networked printer or time clock,
could provide an entry point for lateral movement.
●
Isolating critical systems (e.g., servers and
PCI devices) prevents unauthorized access from potentially infected user
workstations.
●
Restricting guest and employee personal devices ensures they cannot communicate with sensitive internal systems.
By implementing segmentation, businesses
enhance security, reduce attack surfaces,
and enforce strict access policies while maintaining network efficiency.
