Introduction
Networking is one of those things you don’t notice when it’s working but immediately hear about when it’s not. In Azure, the foundation of networking is built on Virtual Networks (VNets), subnets, and firewalls. These three pieces work together to organize, connect, and secure resources.
For system administrators, understanding how they fit together is essential. It ensures you can design cloud environments that perform well and remain secure. For recruiters, this knowledge signals that you don’t just spin up resources — you know how to connect and protect them in a way that aligns with both technical and business needs.
Virtual Networks: The Private Cloud Backbone
A Virtual Network (VNet) in Azure is your private network space in the cloud. It acts much like the traditional networks you’d manage on-premises but with the flexibility and scalability of cloud infrastructure.
VNets provide:
- Isolation: Each VNet is separate from others unless you explicitly connect them.
- Secure communication: Resources such as VMs, databases, and apps can talk to each other safely.
- Hybrid connectivity: You can extend your corporate network into Azure using VPN or ExpressRoute.
Think of a VNet as a private neighborhood. It keeps your workloads together and secure, while still allowing controlled access to the internet or other “neighborhoods” when needed.
Subnets: Organizing the Neighborhood
A VNet on its own is useful, but most organizations need more structure. That’s where subnets come in. They divide a VNet into logical sections, making it easier to apply policies and secure resources.
Why subnets matter:
- Separation of roles: Keep your web servers, application servers, and databases in different subnets.
- Granular security: Network Security Groups (NSGs) can be applied at the subnet level to allow or block specific traffic.
- IP management: Breaking down address spaces into smaller ranges avoids chaos and IP conflicts.
A good analogy is zoning laws in a city. Residential areas, business districts, and industrial zones all exist in the same city but have different rules and protections. Subnets bring that same organization to your Azure environment.
Firewalls: The Security Gate
Even with VNets and subnets in place, you need a strong gatekeeper. The Azure Firewall serves this role. It inspects traffic, applies rules, and blocks malicious actors before they get anywhere near your workloads.
Azure Firewall provides:
- Centralized control: Define rules once and apply them across your environment.
- Filtering: Block or allow traffic based on applications, networks, and ports.
- Threat intelligence: Built-in intelligence to block known bad IPs and domains.
- Integration: Works seamlessly with Azure Monitor and Sentinel for visibility and threat response.
If the VNet is your neighborhood and the subnets are the districts, the firewall is the guard post that checks IDs before anyone comes in.
Real-World Example
A mid-sized retailer moved its e-commerce platform to Azure but initially placed everything in one flat network. This meant the web front end could directly access the database, and unnecessary ports were open. It was functional but risky.
After reworking the design:
- They segmented resources into three subnets: web, application, and database.
- Network Security Groups restricted traffic between these tiers, so only the application subnet could reach the database.
- An Azure Firewall was deployed to filter internet traffic and provide centralized logging.
The outcome was better performance, stronger compliance posture, and fewer late-night calls about suspicious traffic. From a recruiter’s point of view, this shows the administrator had not only the technical skills to fix the problem but also the foresight to align the design with security and business requirements.
Best Practices for Administrators
- Plan IP address ranges carefully before deployment to avoid conflicts later.
- Use subnets to group workloads logically by function or sensitivity.
- Apply layered security: combine Network Security Groups with Azure Firewall.
- Enable monitoring and logging so you can detect issues quickly.
- Keep network diagrams and documentation updated for both technical staff and auditors.
Conclusion
VNets, subnets, and firewalls form the foundation of Azure networking. They bring order, security, and scalability to the cloud.
For administrators, mastering them means being able to design and manage environments that aren’t just functional but secure and compliant. For recruiters, this skill set signals that you understand the backbone of cloud infrastructure and can apply it in a way that supports both technical needs and business goals.
And when you’re interviewing, being able to say “I designed segmented VNets with firewall protection to meet compliance standards” carries much more weight than “I opened a port so the app would work.”