Let's Talk Cloud: Configuring and Managing Virtual Networking in Azure

Hey cloud explorers! Welcome back to our "Let's Talk Cloud" series. Today, we're diving into something that's absolutely fundamental to your Azure environment—virtual networking. While it might not be the most exciting topic at first glance, getting your networking right is crucial for security, performance, and connectivity in the cloud.

Why Virtual Networking Matters

Think of Azure Virtual Networks (VNets) as the digital highways and neighborhood streets of your cloud environment. They determine how your resources communicate with each other, with the internet, and with your on-premises networks. Get them right, and everything flows smoothly. Get them wrong, and you could face security vulnerabilities, performance bottlenecks, or complete communication breakdowns.

The best part? Azure gives you incredible flexibility to design your network architecture exactly how you need it, without the hassle of physical hardware.

Virtual Networks: The Foundation of Azure Networking

Let's start with the basics—Azure Virtual Networks (VNets). A VNet is a logical isolation of the Azure cloud dedicated to your subscription. It's your own private section of Azure, complete with:

- Your own IP address space (using private IP ranges)

- The ability to divide that space into subnets

- Control over DNS settings

- Connection to other VNets and on-premises networks

Creating a VNet is one of the first steps in building your Azure environment. When setting up a VNet, you'll need to decide:

- Address space: Typically using private ranges like 10.0.0.0/16, 172.16.0.0/12, or 192.168.0.0/16

- Subnets: Logical divisions of your address space for different types of resources

- Region: VNets are regional resources, so choose the Azure region that makes sense for your workload

- Subscription: Which Azure subscription the VNet belongs to

Pro tip: Plan your address space carefully! Changing it later can be painful, especially if you need to connect to other networks. I always recommend using a larger address space than you think you'll need (like /16) and then dividing it into subnets.

Subnets: Organizing Your Network

Subnets allow you to segment your VNet into smaller networks. This segmentation helps with:

- Security: Isolating different types of resources

- Network traffic management: Controlling flow between segments

- Resource organization: Grouping similar resources together

When creating subnets, consider organizing them by function or security level:

- Web/frontend subnet

- Application/middle tier subnet

- Database/backend subnet

- Management subnet (for jump boxes or bastion hosts)

- Gateway subnet (for VPN or ExpressRoute connections)

Remember that some Azure services require dedicated subnets with specific names, like "GatewaySubnet" for VPN Gateways or "AzureBastionSubnet" for Azure Bastion.

Network Security Groups (NSGs): Your Network Firewall

Now that we have our network structure, we need to control traffic within it. Network Security Groups act as virtual firewalls, allowing you to filter network traffic to and from Azure resources.

NSGs contain security rules that allow or deny inbound or outbound traffic based on:

- Source and destination IP address/range

- Protocol (TCP, UDP)

- Source and destination port range

- Priority (lower numbers are processed first)

You can apply NSGs at two levels:

1. Subnet level: Controls traffic for all resources in the subnet

2. Network interface level: Controls traffic for a specific resource

My recommendation? Start with NSG rules at the subnet level for broader control, and only use NIC-level NSGs when you need exceptions for specific resources.

Public IP Addresses: Your Gateway to the Internet

If you want your resources to be accessible from the internet or for them to communicate outbound to internet services with their own IP, you'll need public IP addresses.

Azure offers two types:

- Dynamic: The IP address may change when the associated resource is stopped and started

- Static: The IP address remains the same even when the resource is stopped

And two SKUs:

- Basic: Lower cost, no zone redundancy

- Standard: Zone-redundant, works with Standard Load Balancer

When should you use static vs. dynamic? Use static IPs for:

- DNS records pointing to Azure resources

- IP allow-listing for external services

- SSL certificates tied to a specific IP

- Consistent external-facing endpoints

For everything else, dynamic IPs can save costs and management overhead.

DNS in Azure: Naming Your Resources

Every cloud network needs a way to resolve names to IP addresses. Azure provides several DNS options:

- Azure DNS: A hosting service for DNS domains that provides name resolution using Microsoft infrastructure

- Private DNS Zones: Provides name resolution for VMs within a VNet and across VNets

- Default Azure-provided DNS: Automatic name resolution for resources within the same VNet

Setting up Private DNS Zones is particularly useful for internal application naming. For example, you could have your web servers accessible at `web.internal.contoso.com` and your database at `db.internal.contoso.com`, all without exposing any DNS records to the public internet.

Connecting VNets: VNet Peering

As your Azure footprint grows, you'll likely need to connect multiple VNets together. VNet peering creates a direct connection between two VNets, allowing resources to communicate as if they were in the same network, with low latency and high bandwidth.

Peering comes in two flavors:

- Regional peering: Between VNets in the same region

- Global peering: Between VNets in different regions

Peering is not transitive—if VNet A is peered with VNet B, and VNet B is peered with VNet C, resources in VNet A cannot communicate with resources in VNet C unless you specifically peer VNet A and VNet C.

This non-transitive nature is actually a security feature, as it prevents unintended network access paths.

Connecting to On-Premises: Hybrid Networking

Most organizations don't go 100% cloud overnight. You'll likely need to connect your Azure environment to your on-premises networks. Azure offers several options:

Site-to-Site VPN

Creates an encrypted tunnel between your on-premises VPN device and an Azure VPN Gateway. It's perfect for:

- Smaller branch offices

- Dev/test environments

- Lower-throughput requirements

ExpressRoute

Provides a private, dedicated connection to Azure (not over the public internet). Use this for:

- Large-scale migrations

- High-throughput needs

- Lower-latency requirements

- Enhanced security and reliability

Point-to-Site VPN

Allows individual users to connect to your Azure VNet from remote locations. Great for:

- Remote workers

- Small teams

- Managing resources without exposing management ports to the internet

Advanced Networking Features

Once you've mastered the basics, Azure offers several advanced networking features worth exploring:

Azure Firewall

A managed, cloud-based network security service that protects your Azure Virtual Network resources with:

- Built-in high availability

- Unrestricted cloud scalability

- Application and network level filtering

- Threat intelligence

Azure Bastion

A fully managed PaaS service that provides secure RDP and SSH access to your VMs directly from the Azure portal:

- No public IP needed on your VMs

- Protection against port scanning

- Hardened service against zero-day exploits

- Simplified secure access management

Virtual WAN

A networking service that brings many networking, security, and routing functionalities together to provide a single operational interface:

- Global transit network architecture

- Branch connectivity (VPN/SD-WAN)

- ExpressRoute connectivity

- VNet connections

- VPN (site-to-site)

- VPN (point-to-site)

- Routing

- Azure Firewall

- Encryption for private connectivity

Monitoring and Troubleshooting Your Network

Even with perfect planning, network issues can arise. Azure provides several tools to help:

- Network Watcher: Provides network monitoring and diagnostics tools

- Connection Monitor

- IP flow verify

- NSG flow logs

- Packet capture

- Next hop troubleshooting

- Azure Monitor for Networks: Provides a comprehensive view of network health and metrics

My troubleshooting tip: Start with checking NSG rules! In my experience, most connectivity issues in Azure stem from overly restrictive NSG rules or missing rules altogether.

Have you started designing your Azure network? What challenges have you faced? Drop a comment below—I'd love to hear about your experiences!

Until next time, keep your packets flowing and your networks secure!