Why VNets Matter
Every Azure workload depends on networking. Virtual Networks (VNets) are the foundation of Azure networking, providing isolation, segmentation, and secure connectivity for resources.
As a Solution Architect, you must design VNets to balance security, scalability, performance, and integration with on-premises networks.
Core Concepts
1. Virtual Network Basics
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Logical isolation of Azure resources.
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Supports private IP addressing, subnets, and routing.
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Provides network-level security (NSGs, firewalls).
2. Subnets
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Divide VNets into smaller address spaces.
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Assign resources (VMs, services) to subnets.
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Enable delegation (e.g., subnet dedicated to App Service Environment).
3. Address Space (CIDR)
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VNets use private IP ranges (RFC1918: 10.x, 172.16.x, 192.168.x).
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Must avoid overlap with on-premises networks if hybrid connectivity is required.
4. Name Resolution
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Default = Azure-provided DNS.
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Custom = integrate with on-premises DNS servers.
Design Best Practices
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Plan IP Addressing Early
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Choose CIDR ranges that avoid conflicts with corporate on-prem networks.
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Leave room for growth (don’t make address ranges too small).
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Subnet Segmentation
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Group resources by function (Web, App, DB).
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Apply security at subnet level with NSGs.
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Isolate Sensitive Workloads
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Use dedicated subnets for critical services.
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Combine with Azure Firewall or NSGs for protection.
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Scalability
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VNets can be peered across regions.
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Use hub-and-spoke model for large enterprises.
Example Enterprise Scenario
A bank is deploying workloads in Azure:
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Needs separation for web servers, app servers, and databases.
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Requires hybrid connectivity with corporate datacenter.
Correct design:
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Create a VNet with multiple subnets (Web, App, DB).
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Use a non-overlapping IP range with corporate network.
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Apply NSGs to restrict DB subnet to only App subnet traffic.
Confusion Buster
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VNet vs Subnet:
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VNet = overall network boundary.
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Subnet = segment inside the VNet.
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VNet vs Resource Group:
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VNet = network boundary.
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RG = management boundary for resources.
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Azure DNS vs Custom DNS:
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Azure DNS = default, limited features.
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Custom DNS = required for hybrid/on-prem integration.
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Exam Tips
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“Which Azure resource provides logical isolation of networks?” → VNet.
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“How to prevent overlap with on-prem?” → Plan CIDR carefully.
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“How to separate workloads inside a VNet?” → Subnets.
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“Which DNS service resolves names across on-prem and Azure?” → Custom DNS integration.
What to Expect in the Exam
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Direct Q: “Which construct divides a VNet into smaller ranges?” → Subnets.
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Scenario Q: “Company requires separation of web and DB traffic inside a VNet.” → Subnets + NSGs.
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Trick Q: “VNets use public IP ranges only.” → False (private IP ranges).