Conceptualizing Virtual Networks

This lesson explains the foundational networking concept in Azure:

• Azure Virtual Network
• An Azure Virtual Network (VNet) is the core networking boundary in Azure — comparable to your on-premises private network.

1️⃣ What Is an Azure Virtual Network?#

A Virtual Network (VNet):

• Isolated private network in Azure
• Uses private IP address space (RFC 1918)
• Hosts IaaS and integrates PaaS services
• Supports hybrid connectivity

Think of it as:

• Your private data center network
• → but inside Azure

2️⃣ What Can a VNet Connect?#

VNets enable integration with:

✔ IaaS Services#

• Azure Virtual Machines
• Virtual Machine Scale Sets
• Network Virtual Appliances

✔ PaaS Services#

Via Service Endpoints

Via Private Endpoints

✔ Hybrid Environments#

• Site-to-Site VPN
• ExpressRoute
• VNet Peering

3️⃣ Core Components of a Virtual Network#

1️⃣ Address Space#

Every VNet must define:

• RFC 1918 private IP range

Example:

• 10.0.0.0/16
• 172.16.0.0/16
• 192.168.0.0/16
• This defines the total IP pool available.
• Important: You cannot overlap address spaces when connecting VNets or hybrid networks.

2️⃣ Subnets#

Subnets are:

• Segments of VNet address space
• Used to group workloads
• Security and routing boundaries

Example:

• 10.0.0.0/16
• ├── 10.0.1.0/24 (Web)
• ├── 10.0.2.0/24 (App)
• └── 10.0.3.0/24 (DB)

Each subnet:

• Assigns IPs to resources
• Can have NSGs
• Can have route tables
• Can enable service endpoints

3️⃣ Connected Devices#

Connected devices include:

• Virtual Machines
• NICs
• Load Balancers
• Bastion
• Private Endpoints

Each connected device receives:

• ✔ Private IP (via Azure DHCP) ✔ Optional Public IP

4️⃣ Private IP Addressing (DHCP)#

Azure provides:

• Managed DHCP
• Automatic IP assignment
• DNS configuration distribution

Important:

• You cannot deploy your own DHCP server to replace Azure DHCP for VM IP assignment.

5️⃣ Public IP Association#

A resource may have:

• Private IP (inside VNet)
• Public IP (internet accessible)

Public IP is attached to:

• Network Interface
• Load Balancer
• NAT Gateway
• Security Best Practice: Avoid unnecessary public IPs.

6️⃣ Routing in VNets#

Azure provides:

System Routes (Default)#

These are:

• Automatically created
• Immutable
• Control traffic within VNet and internet

Examples:

• VNet local route
• Default internet route (0.0.0.0/0)

Custom Routes (User Defined Routes – UDRs)#

You can:

• Override system routes
• Send traffic to NVA (firewall)
• Control hybrid routing

Route types:

• Virtual Appliance
• Internet
• VNet Peering
• Service Endpoint
• BGP propagated routes

7️⃣ DNS Settings#

By default:

• Azure provides internal DNS (168.63.129.16)

Options:

• ✔ Azure-provided DNS ✔ Custom DNS servers ✔ Domain controllers in subnet
• If using AD DS: You must configure custom DNS settings.

4️⃣ Hybrid Connectivity Options#

VNets support:

• Azure VPN Gateway
• Azure ExpressRoute

This allows:

• On-prem ↔ Azure network extension
• Important: Address space must not overlap.

5️⃣ VNet as Security Boundary#

VNets provide:

• ✔ Isolation from other Azure customers ✔ Segmentation via subnets ✔ Network Security Group enforcement ✔ Routing control ✔ Private connectivity

Think of VNet as:

• Layer 3 boundary in Azure.

6️⃣ Common Exam Concepts (AZ-104 / AZ-700)#

🔹 VNet must have non-overlapping IP space 🔹 Subnets cannot overlap 🔹 Azure DHCP is managed 🔹 System routes cannot be removed 🔹 Custom DNS overrides Azure DNS 🔹 Public IP is optional

7️⃣ Architectural Pattern Example#

Typical 3-tier architecture:

• Internet → Public Load Balancer → Web Subnet → App Subnet → DB Subnet

Optional:

• Hybrid connectivity via VPN Gateway.

8️⃣ Design Best Practices#

✔ Plan address space carefully ✔ Avoid overlapping IP ranges ✔ Use subnet segmentation ✔ Minimize public IP usage ✔ Use NSGs per subnet ✔ Use UDRs for traffic inspection ✔ Use private endpoints for PaaS

9️⃣ Troubleshooting Scenarios#

If VM cannot communicate:

• Check subnet placement
• Check NSGs
• Check route tables
• Verify DNS configuration
• Confirm IP address assignment

🔟 Reference Documentation#

• Virtual Network Overview
• IP Address Planning
• Routing Overview
• DNS in Azure
• Hybrid Connectivity

Final Conceptual Summary#

Azure Virtual Network is:

• Your isolated private cloud network
• Built on RFC 1918 address space
• Segmented into subnets
• Controlled by routing & NSGs
• Integrated with IaaS, PaaS, and hybrid
• Everything networking-related in Azure starts with VNet.

If you'd like, I can now create:

• 🧠 30 VNet exam questions
• 📊 Visual comparison of VNet components
• 🏗 Hub-Spoke architecture deep dive
• 📄 One-page AZ-104 networking cheat sheet
• Tell me which certification you’re targeting next.